Given: y varies directly as x. If y = 5 when x = 4, what is the value of y when x = 12?

Direct Variation: y = kx. Plugging in 5 as y and 4 as x, we get 5 = 4k, k = 5/4.
Now we can find y: y = (5/4)(12) = 15, so y = 15.
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