We can simplify this to 3a + 4b = 2a - 6b + 24. Then, we subtract 2a from both sides and 4b from both sides. This leaves us with a = -10b + 24. Then, we switch a and -10b. This turns into 10b = 24 - a. Divide 10 from both sides, and it gives us b = 12 / 5 - a / 10