What is 3x+3y=-18 when y=2x

Hello there!

To start, since you already know that the value of y equals 2x, you can plug 2x in place of y in 3x+3y=-18. This would look like this:

3x+3 (2x) = - 18

Now simplify:

3x+6x=-18

Now, combine your like terms:

9x=-18

And divide both sides by 9 to solve for x:

x=-2

Now that you have x=-2, you can plug that back into y=2x where you plug in - 2 in place of x:

y=2 (-2)

y=-4

Therefore, your x=-2 and your y=-4 which would be your final answer.