Expand
x = 150 - 0.5x
Add 0.5x to both sides
x + 0.5x = 150
Simplify x + 0.5x to 1.5x
1.5x = 150
Divide both sides by 1.5
x = 150/1.5
Simplify 150/1.5 to 100
x = 100
