Question

If you were to use the substitution method to solve the following system, choose the new equation after the expression equivalent to x from the second equation is substituted into the first equation.

3x + 2y = -21
x - 3y = 4
Choose one answer.
A. 3(3y + 4) + 2y = -21
B. 3(-3y + 4) + 2y = -21
C. 3x + 2(3y + 4) = -21
D. 3x + 2(-3y + 4) = -21

Answer 1

If you want to make the second equation equivalent to x, that means you are solving it for x. So it would look like this:
x = 3y + 4

Answer 2

You will use that value of x and sub it into the first equation where you see the x, like this:
3(3y+4) + 2y = -21

Answer 3

It's choice A.