Let's first judge who is more anxious to solve these two things.
If you go to the library to study, it is necessary to do textual research and postgraduate entrance examination. In the near future, there is an urgent need to go to the library to study. It doesn't matter if the teacher calls for help, such as asking you to get a courier or going to the office to help clean up, that's a normal event. Obviously, by contrast, it is more urgent to study in the library. Therefore, at this time, you can directly refuse the teacher and explain your current situation. Of course, you can also find other reasons to refuse the teacher.
Maybe you will worry that the teacher will blame you. In fact, you don't have to worry about the teacher not understanding. Teachers generally don't care about such trifles, and there are many students' contact information. If you can't help, they will ask other students for help.
Second, judge whether what the teacher asks for help is official or private.
When judging the public and private nature of things, we need to talk about the identity of students themselves. Here is an example. If a student is a student reporter of the Party Committee of the school, or an officer of the Propaganda Department of the Student Union, and the teacher wants to attend an important activity of a school and asks you to help shoot a report, then this matter is official business and your duty. If you can't go at this time because of something, then you should also share the teacher's troubles about how to solve this matter. The best way is to find other students, journalists or officers to shoot instead of you at once. If you really can't find someone to replace you, you'll have to solve it yourself.
Of course, if you think it is more important to study in the library than to fulfill the duties of a student reporter or an officer, then you can also refuse. However, you should also be prepared, because of dereliction of duty, you will lose the trust of the teacher, or even be expelled from the teacher's status as a student reporter or an officer.
Third, judge whether this matter belongs to your responsibility and obligation.
If the teacher asks you for help is a private matter, but this private matter involves your responsibilities and obligations, then you also need help at this time. For example, if you are a class cadre, the teacher asks you to help visit a classmate who is ill in hospital. This matter is a private matter, but at the same time, because you are a class cadre and represent the image and mind of the class, you should promise the teacher help at this time.
Of course, if you go to the library to study this matter and it affects your participation in some competitions or your application for graduation, then you can make it clear to the teacher and contact other class cadres in the class to help the teacher finish this matter. In short, proper arrangements should be made to meet the needs of teachers without violating their status as class cadres to assume responsibilities and obligations.
Fourth, judge whether you are willing to help.
If you are not a class cadre or a member of any student union or society, you are just an ordinary student. Then when the teacher asks you for help to do something and you want to go to the library to study, you can measure how much time and energy it takes and ask yourself: Are you willing to help? If the answer is yes, then help. No matter what unpleasant things happen in the process, don't complain afterwards. If the answer is no, then find a reason to refuse the teacher and study hard in the library.
In a word, we can judge "I want to go to the library to study, but my teacher asked me to help" from the dimensions of urgency, public and private nature, responsibility and obligation, and willingness. After weighing the pros and cons, if you clearly don't want to help, you should also have the courage to refuse and the ability to say "no". After all, some students don't want to go or don't need to go, but because of their "please-type" personality, they make choices against their wishes. As a result, they can't please the teacher and wronged themselves, which is not worth the loss.