SAT Question 87a3de81: Nonlinear Equations In One Variable And Systems Of Equations In Two Variables answer and explanation with Desmos solution

The solution to the given equation can be found by factoring the quadratic expression. The factors can be determined by finding two numbers with a sum of $1$ and a product of $-12$. The two numbers that meet these constraints are $4$ and $-3$. Therefore, the given equation can be rewritten as $(x+4)(x-3)=0$. It follows that the solutions to the equation are $x=-4$ or $x=3$. Since it is given that $a>0$, $a$ must equal $3$.