Question

THE SUM OF A NUMBER, X
AND 9 is 21.
SOLVE FOR X.

Answer 1

12

Explanation:

To get the answer 12 you must:

Subtract 21 - 9

That would get you your answer.

Answer 2

X + 9 = 21

Isolate the variable, meaning getting rid of the constants

-9 -9

X = 12