The way I read this problem, following the bearing "from A to B" takes you from Point A to Point B. Following the bearing "from B to A" takes you from Point B back to Point A. So, imagine going from A to B, and then wanting to go back to A. What do you do? At Point B, you turn around, which we commonly think of as "doing a 180;" in other words, turning 180o.
Thus, to get the bearing from B back to A, you just have to take your bearing from A to B and add 180o. So, 40 + 180 = 220o for the first. Then 120 + 180 = 300 degrees for the second.
For the third, I agree with Kenneth, that this means 20 degrees west of north. If you draw a standard set of x-y (Cartesian) axes, you can label the +x axis as east, then going around to north (+y axis), west (-x axis) and south (-y axis). By this reckoning, 20 degrees west of north means veer 20 degrees to the west of due north, as Kenneth said.
In my experience, angles are conventionally measured from the +x axis counterclockwise (in other words, starting at die east and then swinging around counterclockwise. By this reckoning, an angle 20 degrees west of due north would be 90 degrees (the angle from east to north) plus the additional 20 degrees past north, heading towards west, so 90 + 20 = 110 degrees
But I would defer on the last question to those who are more experienced with compass directions.