Suppose two children push horizontally, but in exactly opposite directions, on a third child in a sled. The first child exerts a force of 74 N, the second a force of 99 N, kinetic friction is 7.5 N, and the mass of the third child plus sled is 23.5 kg.

part a. Using a coordinate system where the second child is pushing in the positive direction, calculate the acceleration in m/s².