The second question: don't think too complicated, you can get to the point. 9*48÷ 16

The third question: the distance is fixed, so the speed ratio is inversely proportional to time. Up 60, down 80. That is, the speed of going up the mountain is 3, and the speed of going down the mountain is 4, so it takes 4 times to go up the mountain and 3 times to go down the mountain. So, 60*4=80*3, you know. Teachers should emphasize this point in class. If you still don't understand the above, it means that your basic department is solid and the relationship between addition, subtraction, multiplication and division is not very clear and thorough. You need to think more for yourself. Especially when you were in the fifth grade, you did badly in the exam and the meaning of the score was not solid. Practice more.

(Professional teachers teach, absolutely rest assured. )