This is about direct variation. If y varies directly with x, then there is a constant factor of variation, k. The constant of variation can be found by ʸ⁄ₓ
k = ʸ⁄ₓ
k = ¹⁵⁄₅ = 3
Now that we have found k, we simply multiply x by it to find y (this is because y is directly proportional to x). We plug in our x = 7 to find y at this point.
