Cost of Lightbulb = x
cost of switch is x-8
9x + 4(x-8) = 520.50
Use distributive property:
9x + 4x -32 = 520.50
Simplify:
13x -32 = 520.50
Add 32 to both sides:
13x = 552.50
Divide both sides by 13
X = 42.50
A lightbulb costs $42.50
A switch costs 42.50-8 = $34.50