# The variables x=-6 and y=15 varies directly. How do you write an equation that relates the variables and find y when x=8?

##### 1 Answer

May 2, 2017

Solve a proportion.

#### Explanation:

If x and y vary directly, it means y = kx, where k is the constant of proportionality.

For any pair (x, y), we have

We have (-6, 15) as one set of values, and we have (8, y) as another -- where y is unknown. Solve the proportion:

Finish the problem by "cross-multiplying", and solving for y. You should get y = -20.