3a+30-12=75 how do you do this

Answer 1

3a+30-12=75
you combine 30-12 and get:
3a+18=75
then you subtract 18 from both sides:

3a-18=75-18

and get:

3a=57

then divide both sides by 3
3a/3=57/3
a=19

So 'a' equals 19

Answer 2

The previous answer is correct, but this subject is NOT geometry.