Answer
y=12
Step-by-step explanation:
y+9=21 (this would be the formula)
-9 -9 (you want to eliminate 9 from the equation, so subtract it from both sides of the equation)
y=12 (after subtracting 9 from both sides you are left with 12)
Check it
12+9=21 (is this true?)
21=21 (yes it is true, therefore y=12)
