SAT Question 69f609b2: Linear Equations In One Variable answer and explanation with Desmos solution

Choice A is correct. Distributing $12$ on the left-hand side and $-3$ on the right-hand side of the given equation yields $12x-36=-3x-36$. Adding $3x$ to each side of this equation yields $15x-36=-36$. Adding $36$ to each side of this equation yields $15x=0$. Dividing each side of this equation by $15$ yields $x=0$. This means that $0$ is the only solution to the given equation. Therefore, the given equation has exactly one solution.