If x varies directly as y, and x=18 when y=6 find x when y = 10!

First thing you need to do is find your k in y = kx

So to do that insert 18 for x and 6 for y and then solve for k

y = kx

6 = k18

6/18 = k18 / 18

1 / 3 = k

k = 1 / 3

So now that we know what k is we can find x when y = 10. Once again insert the numbers we know. We know k = 1/3 and y = 10 and we need to find x

y = kx

10 = (1/3) x

3 * 10 = 3 * (1/3) x

30 = x

x = 30