To solve for x, you need to isolate/get "x" by itself in the equation
3x + (8x + 15) = 180 Add 3x and 8x
11x + 15 = 180 Subtract 15 on both sides
11x + 15 - 15 = 180 - 15
11x = 165 Divide 11 on both sides
[tex]x = \frac{165}{11}[/tex] Simplify
x = 15
PROOF
3x + (8x + 15) = 180 Plug in 15 for x
3(15) + 8(15) + 15 = 180
45 + 120 + 15 = 180
60 + 120 = 180
180 = 180
