A 20 kg box initially at rest on a rough horizontal surface is pushed by a constant horizontal force of 150 N for 3.0 s. The coefficient of kinetic friction between the box and the surface is 0.25. What is the speed of the box at the end of the 3.0 s interval?
a) 17m/s
b) 15m/s
c) 22.5m/s
d) 12m/s