d - 30 d + 30 - 7 = - 7 What is a solution to

The correct answer is either $-30$ or $30$. 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.