The equation −3x−9=−21 is solved as follows. Supply the correct numbers to complete the solution

add 9 to both sides, -3x=

-21 + 9

-21 + 9 = -12

Therefore, -3x = -12

To solve the equation −3x−9=−21, you need to isolate x on one side of the equation. The first step is to eliminate the constant term -9 on the left side of the equation.

To do this, add 9 to both sides of the equation:

-3x - 9 + 9 = -21 + 9

On the left side of the equation, -9 + 9 equals 0, so it cancels out. On the right side of the equation, -21 + 9 equals -12.

Therefore, the equation becomes:

-3x = -12

Now, you have successfully completed the first step of the solution!