1. Distribute the 9.
27x - 144 + 15 = 6x - 24
2. Combine like terms
27x - 129 = 6x - 24
3. Gather all the terms with x on the left, and all the constants on the right. We do this by subtracting 6x and adding 129 to both sides.
21x = 105
4. Divide both sides by 21
x = 21
So, x = 21 makes the equation true.