SAT Question 364a2d25: Nonlinear Equations In One Variable And Systems Of Equations In Two Variables answer and explanation with Desmos solution

The first equation can be rewritten as $y=17-x$. Substituting $17-x$ for $y$ in the second equation gives $x\times (17-x)=72$. By applying the distributive property, this can be rewritten as $17x-x^2=72$. Subtracting $72$ from both sides of the equation yields $x^2-17x+72=0$. Factoring the left-hand side of this equation yields $(x-8)\times (x-9)=0$. Applying the Zero Product Property, it follows that $x-8=0$ and $x-9=0$. Solving each equation for $x$ yields $x=8$ and $x=9$ respectively. Note that 8 and 9 are examples of ways to enter a correct answer.