X=1/3(90-x) What is x?
X=1/3(90-x)
3X=90-X
4X=90
X=90/4
X=22.5
x=1/3(90-x)⇒3x=90-x⇒4x=90⇒x=22.5 (or 22,5, it depends on where you are from)