The flatbed truck, which carries an 80 kg crate, starts from rest and attains a speed of 20m/s in a distance of 75m on a level road with constant acceleration. Calculate the work done by the frictional force acting on the crate during this interval if the static and kinetic friction coefficients of friction between the crate and truck bed are a) .3 and .28, respectively, or b) .25 and .20 respectively.