Begin the problem by solving for y with the second equation. Add -4x to both sides of the equation so it reads y=4x+21. Then, substitute y into the first equation and solve. -2x-3(4x+21)=-7 turns into -14x-63=-7, which becomes -14x=56. Divide 56/-14 to get -4 for x. Since only one answer has -4 as an option for x, that's the correct answer.
