#### Answer

The solution set is {0, -9}.

#### Work Step by Step

For this problem, we can factor out an $x$ to simplify it:
$$x(x + 9) = 0$$
According to the zero product property, the product of factors is zero if at least one factor is zero. Therefore, we can set each factor to zero to solve for $x$:
$$x = 0$$
or
$$x + 9 = 0$$
We subtract $9$ to each side of the equation to solve for $x$:
$$x = -9$$
The solution set is {0, -9}.