Question

how can I solve this?

Answer 1

∠a+108°=180°
so∠a=72°
and ∠b+∠a=90°
so ∠b= 18°

Answer 2

a straight line is measured to be 180 degrees so, 180-108 = 72 degrees for a. then a+b = 90 degrees. b=90-72=18 degrees. :)