Answer:
m<C = 102°
Step-by-step explanation:
Step 1: find measure of arc BC.
According to the Inscribed angle theorem of a circle, an inscribed angle is half the measure of the arc it intercepts.
m<D intercepts arc ABC
thus, 80° = ½(120+BC)
Solve for BC. Multiply both sides by 2
80*2 = 120 + BC
160 = 120 + BC
BC = 160 - 120 = 40°
Step 2: Find m < A
According to the Inscribed angle theorem, m < A = ½ of arc BCD = ½(40 + 116)
m < A = 78°
Step 3: find m < C
m < A + m < C = 180 (opposite angles of an inscribed quadrilateral are supplementary)
m < C = 180 - 78 = 102°
