You fire a paintball from a paintball gun straight up into the air at 25.0 m/s What is the instantaneous velocity at the top of its flight?

The instantaneous velocity at the top of its flight is  v = 0 m/s

Explanation:

From the question we are told that

   The  initial velocity is u = 25.0 m/s

Generally an  instantaneous velocity can be defined as the velocity of an object at an instant of  time period during its motion, , generally the velocity of a object at it maximum height is  0 m/s hence the  instantaneous velocity of the paintball at the top of its flight is  0 m/s

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.