What are your questions? If so what type of mathematic class: Algebra, Algebra 2, Geometery, Trigeometery, Pre-calculus, Calculus..
27x - 144 + 15 = 6x - 24
27x - 129 = 6x - 24
+129 +129
--------- --------
0 105
27x = 6x + 105
-6x -6x
----- ------
21x 0
21x = 105
21x/21 = 105/21
x = 5
Remove brackets
Gather like terms
Get rid of the lone number
Transfer
Divide
Hope this helps :)