4U mechanics question - find: maximum speed attained; distance travelled

Please help i have trouble understand this problem and i could not apply appropriate formulae to solve it. I had tried but still obtain the correct answer.

The problem is: A particle of mass 10kg, moving in a straight line, starts at rest from a point A under the action of a force that decreases uniformly from 20N to zero in 20 secs. IT then travels with a constant speed for a further 20s, and finally moves under the action of an opposing force of 40N until it comes to rest at B. Find the maximum speed attained and the distance travelled.