Question

find the missing number so that the equation has infinitely many solutions. -3(-x + 3) = 3x + \square

Explanation:

Step1: Expand left-hand side

$$\begin{align*} -3(-x + 3) &= (-3)(-x) + (-3)(3)\\ &= 3x - 9 \end{align*}$$

Step2: Match constant terms

For infinitely many solutions, both sides of the equation must be identical. The right-hand side is $3x + \square$, so the constant term must equal $-9$.

Answer:

$-9$