For the length of WZ make the ratio 3r+5r = 8r
So the point is 3/8 the way up the line. Find the length by taking the (difference of the x's) and also the (difference of the y's):
(x of Z - x of W) = (40-12) = 28
(y of Z - y if W) = (50-18) = 32
So the point is 3/8 (28) along the x direction and 3/8 (32) along the y direction
Therefore the point should be at (x, y) of:
(3/8×28, 3/8×32) = (10.5, 12)