Algebra 1 systems of equations help

I need help with this problem:

For the following system, if you isolated x in the second equation to use the Substitution Method, what expression would you substitute into the first equation?

5x + 3y = 9
3x + 6y = 18

Just solve the second equation for x.

3x + 6y = 18
3x = 18 - 6y
x = 6 - 2y

You would substitute x as being the equation 6 - 2y in the first equation to solve for the values.

Cheers!

OK

5x + 3y = 9
3x + 6y = 18

Isolating x in the second equation would look like this:
3x = 18 - 6y
x = 6 - 2y

Now you can substitute this value of x in the first equation:

5(6-2y) + 3y = 9
30 - 10y + 3y = 9
-7y = -21
y = 3

We know x = 6-2y
x = 6-2(3)
x = 6-6
x= 0

So the answers are x=0. y = 3.

Prove it by placing both in the second equation:
3(0) + 6(3) = 18??
0 + 18 = 18 ??
18 = 18 YES!!

Hope that helps.

3x + 6y = 18
3x = 18 - 6y
x = 6 - 3y
So, you would plug 6 - 3y
5(6 - 3y) + 3y = 9

-2y+6 so C