First, distribute 8 to 3a and 6, and distribute 9 to 2a and -4
8(3a + 6) = 24a + 48
9(2a - 4) = 18a - 36
24a + 48 = 18a - 36
Isolate the a. Subtract 48 and 18a from both sides. (Note the equal sign. What you do to one side, you must do to the other.
24a (-18a) + 48 (-48) = 18a (-18a) - 36 (-48)
24a - 18a = -36 - 48
Simplify.
6a = -84
Isolate the a. Divide 6 from both sides
6a/6 = -84/6
a = -84/6
a = -14
-14 is your answer for a
hope this helps