Question

Find the measure of ∠C if

∠A = 3/2x + 20
∠B = 7/2x + 20
∠C = 5/2x + 40
∠D = 3/2x + 10
A) 65°
B) 76°
C) 95°
D) 115°

Answer 1

The sum of angles is 360°
Thus:
∠A+∠B+∠C+∠D=360
(3/2x+20)+(7/2x+20)+(5/2x+40)+(3/2x+10)=360
9x+90=360
9x=270
x=30
thus
∠C = 5/2x + 40=5/2×30+40=115°