Answer:
add 3 to both sides of the equal sign
Explanation:
to solve the equation you would have to add three
that is because you have to do inverse operations
and you would add because the opposite of subtracting is adding
so solving it would look like this
x - 3 = 12
+3 +3
x = 15
this is how you check the answer:
15 - 3 = 12
+3 +3