Question

write an equation that relates x and y. find y when x=6.
x=3, y=9
x=4, y=2
x=5, y=30

Answer 1

You can write any equation you want, or are there conditions?

Answer 2

yes it can be any equation.

Answer 3

If you can write any equation you want, write
y = 3x

Then to find y when x = 6, just substitute x with 6 and calculate y:
y = 3x
y = 3*6
y = 18

Now do the same for x = 3

For the last part, y = 9, it's a little different. Here you substitute y with 9, and you solve for x.
y = 3x
9 = 3x, solve for x by dividing both sides by 3
3 = x
x = 3