If y=15 when x=5, find y when x=7, given that y varies directly with x.

when x = 7, y = 21

Step-by-step explanation:

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.

y = 3x

y = 3(7)

y = 21

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step-by-step explanation: