ecuations.

[input]8x - (3x + 7) = 18[/input]

8x - (3x + 7) = 18
equals to:
8x - 3x - 7 = 18
+7 on both sides
8x - 3x - 7 +7 = 18+7
8x - 3x = 25
5x = 25
/5 on both sides
x = 25/5
x = 5