What is the value of x?
14 - x = 21
x = ?

Solve the equation
To find x, we do inverse operation. Inverse Operation is applying the opposite operation to the lonely number.
14-x=21
Inverse operation for positive 14 is -14
So we must apply that to both sides.
14-x=21
-14     -14
then we have -x=7
Because our variable has a -1x=7, we flip the signs so we get x=-7
So our final answer is x=-7

Check our work
14-x=21
14+7=21
CORRECT ANSWER! :)