Solve 12x = 4(x + 5)
solve 15x - 3(3x + 4) =6
solve 3x - 5x + 10 = 36
solve 2(x+3)= x + 10

12x=4(x+5)     (multiplying 4 by each argument in the parenhesis)
12x=4x+20     /-4x both sides
8x=20  /:8 divide both sides by 8


15x-3(3x+4)=6      (-3 times each argument in the parenthesis)
15x-9x-12=6
6x-12=6             /+12 both sides
6x=18        /:6 divide both sides by 6
x=3

3x-5x+10=36
-2x+10=36     /-10 both sides
-2x=26      /:(-2) divide both sides by -2
x=-13

2(x+3)=x+10
2x+6=x+10      /-x
x+6=10          /-6
x=4