SAT Question 3d7d7534: Nonlinear Equations In One Variable And Systems Of Equations In Two Variables answer and explanation with Desmos solution

Adding $7$ to each side of the given equation yields $\left(d-30\right)\left(d+30\right)=0$. Since a product of two factors is equal to $0$ if and only if at least one of the factors is $0$, either $d-30=0$ or $d+30=0$. Adding $30$ to each side of the equation $d-30=0$ yields $d=30$. Subtracting $30$ from each side of the equation $d+30=0$ yields $d=-30$. Therefore, the solutions to the given equation are $-30$ and $30$. Note that 30 and -30 are examples of ways to enter a correct answer.