Two forces, of magnitudes F_1 = 85.0 N and F_2 = 45.0 N, act in opposite directions on a block, which sits atop a frictionless surface, as shown in the figure. Initially, the center of the block is at position x_i = -4.00 cm. At some later time, the block has moved to the right, and its center is at a new position, x_f = 5.00 cm.

Answer 1

F_1=85*(0.04+0.05)=7.65J
F_2=45*(0.04+0.05)=4.05J

Answer 2

The previous dude is 75% correct. The second answer HAS to be negative since it's moving backwards mate.