Abox rests on a horizontal, frictionless surface. a girl pushes on the box with a force of 17 n to the right and a boy pushes on the box with a force of 13 n to the left. the box moves 3.5 m to the right. find the work done by (a) the girl, (b) the boy, and (c) the net force.

Refer to the diagram shown below.

The net force acting on the box is 17 - 13 = 4 N to the right.
The box moves on a friction surface by 3.5 m to the right.

By definition,
Work = Force x Distance.

(a) The work done by the girl is
     W₁ = (17 N)*(3.5 m) = 59.5 J

(b) The work done by the boy is
     W₂ = (13 N)*(-3.5 m) = - 45.5 J

(c) The work done by the net force  is
    W₃ = (4 N)*(3.5 m) = 14 J

Note that W₃ = W₁ + W₂

Answers:
(a) 59.5 J
(b) - 45.5 J
(c) 14 J