Final answer:
The work done by applying a force of 200 N to move a box 15 m is calculated as 200 N multiplied by 15 m, which equals 3000 J.
Step-by-step explanation:
When a force of 200 N is applied to push a box for a distance of 15 m down the sidewalk, the work done can be calculated using the formula W = F x D, where W is the work done, F is the force applied, and D is the distance over which the force is applied. In this case, the work done is 200 N multiplied by 15 m, which equals 3000 J (joules). The correct answer is therefore a) 3000 J.