Question

Show me how to get an answer for:
1a + 18 = 7a

Answer 1

1a+18=7a
18=7a-1a
18=6a
6a=18
a=18/6
a=3

Answer 2

subtract the 1a from the 7a. 
1a + 18 = 7a
-1a          -1a

you're then left with 18=6a. divide the 6 with the 18 to cancel out.
18=6a
/6a /6a

18 divided by 6 is 3. So your answer is a=3