Question

The variables x and y vary directly, how do you write an equation that relates x and y when given x = -18, y = -2, and then how do you find x when y=4?

Answer 1

I think you can write it as:
`y=kx` where `k` is the constant of proportionality to be found;

use `x=-18` and `y=-2` to find `k` as:

`-2=k(-18)`

so `k=(-2)/(-18)=1/9`

So, when `y=4`:
`4=1/9x`
and `x=36`