What is the measure of ∠C?

Answer: 38 degrees
Step-by-step explanation:
Because arc AB is equal to 76 degrees, angle ADB must also be 76 degrees.
Then simply take the supplement of the angle to get that < CDA is 104 degrees. Because it is part of an isosceles triangle, simply subtract 104 from 180 to get that <A + <C = 74 degrees. Because triangle ADC is isosceles (All radii of a circle are equal), simply divide 76 / 2 to get that <C = 38.
Hope it helps :)
[tex]\qquad \qquad\huge \underline{\boxed{\sf Answer}}[/tex]
Theorem : Angle subtended by an arc on the circumference of the circle is half the angle subtended by the same arc on the center of the same circle.
That is :
[tex] \qquad \sf \dashrightarrow \: \angle \: c = \frac{1}{2} \times 76[/tex]
[tex] \qquad \sf \dashrightarrow \: \angle \: c = 38 \degree[/tex]