Question

next, do the same operation to each side so that 3x remains on the left. then rewrite the equation.
3(x - 7) = -12
3x - 21 = -12
+ □ + 1
□ = □

Explanation:

Step1: Eliminate -21 on left

To leave $3x$ on the left, add 21 to both sides to cancel out $-21$.
$3x - 21 + 21 = -12 + 21$

Step2: Simplify both sides

Calculate the result of each side of the equation.
$3x = 9$

Answer:

Top left box: 21, Top right box: 21
Bottom left box: $3x$, Bottom right box: 9