Question

The value of y varies directly with x, and y = 12 when x = 8.
Find y when x = 15.

Answer 1

It's been a while, but it seems like you need another point... assuming x and y both go through the origin (0,0) then y would be increasing at a rate of (12/8)x which is 1.5x. so if x is 15 then y would be 15*1.5 = 22.5. But then again this is only as good as the assumption that they both go through the origin. I may be missing something.