17 because 4 x 1.5 = 6, 50 / 1.5 = 33.33
A slope of 1/2 means for every two units to the right we move up one.
We have to be careful here because the graphs don't always use the same scale for x and y.
The bottom left uses the same scale and does indeed go two units to the right for every unit up, so that one is the answer.