As y varies directly with x, there is a proportionality constant. As x increases by that certain constant, y also increases. We equate:
y = kx
where k = proportionality constant.
Given the condition, y = 9 when x = 2, then we solve for k:
9 = k(2)
k = 9/2 or 4.5
When x = 3, then
y = (9/2)(3) = 27/2 or 13 ½ or 13.5 (ANSWER)
