To determine the horizontal force required to accelerate a 4.0 kg box with a coefficient of friction of 0.60 at 2.0 m/s², first calculate the friction force using the formula: friction force = coefficient of friction * normal force. The normal force equals the weight of the box, which is 4.0 kg multiplied by gravity (9.81 m/s²), resulting in a normal force of approximately 39.24 N. The total force needed can be found by applying Newton's second law (F = ma), which gives a force of 8 N for acceleration. Adding the friction force to this total yields the necessary horizontal force to overcome friction and achieve the desired acceleration.