Directly proportional means that you have a relationship in the form of y=kx, where x and y would be hip size and waist size respectively. Plug in the given info to solve for k.

You could also do this by ratios. For a 40 in hip size, ideal waist size is 32 in. So the ratio of hip:waist is 40:32. This ratio is the same for any hip and waist size. So 35:x , where the hip size is 35 in and the ideal waist is x has the same ratio as 40:32.

Solve for x.