SAT Question 371cbf6b: Equivalent Expressions answer and explanation with Desmos solution

Choice A is incorrect. If $ab=18$, then the coefficient of $x^2$ on the left-hand side of the equation would be $-18+15=-3$, which doesn't equal the coefficient of $x^2$, $-9$, on the right-hand side.

Choice B is incorrect. If $ab=20$, then the coefficient of $x^2$ on the left-hand side of the equation would be $-20+15=-5$, which doesn't equal the coefficient of $x^2$, $-9$, on the right-hand side.

Choice D is incorrect. If $ab=40$, then the coefficient of $x^2$ on the left-hand side of the equation would be $-40+15=-25$, which doesn't equal the coefficient of $x^2$, $-9$, on the right-hand side.