First in order to calculate this you just have to solve the multiplication of the signs:
-(-1/2)= 1/2
So what you will actually do would be add 1/2 to -1/3, as you know you have to move the point in the line, the line is advancing at 1/6 at a time so -1/3 would be -2/6 so you need to move to the left from 1/2 two stops, and you will end up in 1/6 and that would be the answer.