Check your answers every time you do more exercises. Don't just look at the final result. Step by step, see what the answer is, but you didn't write it. Think more about what they mean. Have you ever thought about asking the teacher if you don't understand? Every time you write a topic, you must first clear your mind, what to write first and then what to write, step by step, so that you can do more exercises. My senior three teacher taught you.