Saving time

A body of weight 70 newton is placed on the start point of a horizontal road of length 300 meter then a force of magnitude 100 Newton acts on the body where the direction of the force is changeable (means that you can change the direction of the force whenever you want during the motion of the body). If the first 100 meter of the road is of friction coefficient 0.5 and the second 100 meter is of friction coefficient 1.3 and the last 100 meter is of friction coefficient 1.8 find the minimum time for the boys to cross the road. Write your answer approximated to five digits after the decimal good luck