The answer is 3 because you have to add 3 on both sides. Then you will get 5x =15 then to get X by itself you would have to divide by 5 on Both sides 5x/5 cancels its self out then your left with x 15/5=3 so you will get X=3 therefor the number is 3
5x-3=12
+3 +3
5x=15
———-
5 5
X=3
