SAT Question 13e5a5d5: Nonlinear Equations In One Variable And Systems Of Equations In Two Variables answer and explanation with Desmos solution

Dividing both sides of the given equation by $5$ yields $|x|=9$. By the definition of absolute value, if $|x|=9$, then $x=9$ or $x=-9$. Therefore, the two solutions to the equation $5\left|x\right|=45$ are $9$ and $-9$. It follows that the positive solution to the given equation is $9$.