Hey everyone... I'm having problems with two questions from my Algebra 2 book. The questions are about Variation Equations.

There are two types of problems that I want to go over so any help is appreciated. Thanks.

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9. y varies directly as x. If x = 4, then y = -12. Find y when x = -7.

11. y varies inversely as the cub of x. If x = 4, y = -1/16. Find y when x = 1/2.