Answer :

11a = 18a + 21
11a - 18a = - 18a + 21
-7a = 21
7a = -21
a = -21/ 7
a = -3
Ok, the points is to isolate the variable "a". First, you subtract 18a from both sides to remove the 18a from the right side, ending up with -7a = 21. Dividing both sides by -7, you will end up with a = -3. Answer: a = -3