Solve the simultaneous equations 3x + 2y = -7 and x=4y+21

Substitute in the second equation into the first to eliminate x from the first equation. Solve for y which should, when solved (shown below), equal -5. Sub -5 back into either equation in the place of y to then solve for x (shown below) x should then equal 1.
3(4y+21) +2y = -7 (solve for y)y = -53x +2(-5) = -7 (solve for x)x = 1