Positive angle that is co-terminal with 120 deg.

One of them is (120 +360) = 480 degrees. ---answer.

Everytime you do 1 revolution (360 deg), you will get one more.

Positive angle that is co-terminal with pi/5.

In radians, 1 revolution is 2pi, so,

One of them is (pi/5 +2pi) = (pi +10pi)/5 = 11pi/5 ---answer.

Everytime you do 1 revolution (2pi), you will get one more.

Negative angle that is co-terminal with 420 deg.

420 deg is (360 +60) deg. It is is the 1st quadrant.

So, measuring clockwise, -360 +60 = -300 degrees ----answer.

Everytime you do 1 revolution (-360deg), you will get another one.

Negative angle that is co-terminal with 3pi/5.

3pi/5 is 0.6pi. It is more than pi/2, but less than pi, so it is in the 2nd quadrant.

Meausing clockwise, -2pi +(3pi/5) = (-10pi +3pi)/5 = -7pi/5 ---answer.

Everytime you do 1 revolution (-2pi), you will get another one.