Can you please help me with the following questions? please.

1. how much work do you do on a 25-kg backpack when you walk a horizontal distance of 100 m?
-I got 2,500 J

4. if you friend pushes a lawnmower four times as far as you do while exerting only half the force, which one of you does more work? how much more? ( I don't understand this question)

7.why does one get tired when pushing against a stationary wall when no work is done on the wall?
-I got because the wall is pushing back with the same equal amount of force.

9. which requires more work streching a strong spring a certain distance or streching a weak spring the same distace? Why?