You hang a book bag on a spring scale and place the bag on a platform scale so that the platform scale reads 29.7 N and the spring scale reads 17.6 N.

Hello. This question is incomplete. The full question is:

You hang a book bag on a spring scale and place the bag on a platform scale so that the platform scale reads 29.7 N and the spring scale reads 17.6 N.

What is the magnitude of the force that Earth exerts on the bag?

47.3 N

Explanation:

the entire system shown in the question above is at rest. Which greatly facilitates the calculation that we must do. In this case, to measure the magnitude that the force of the earth has on the backpack, you only need to add the two forces that you already know in the system.

In that case, it would be, you should calculate:

F= 29.7 N+ 17.6 N

F= 47.3N

the answer is b, have negligible mass