Opposite angles of inscribed quadrilaterals are supplementary.
That means ∠D + ∠B = 180°
So, we can substitute in the given values.
(4x + 3) + (2x + 3) = 180
Solve for x.
4x + 3 + 2x + 3 = 180
6x + 6 = 180
6x = 174
x = 29
We know ∠C = 2x + 1, so we can substitute our value of x in.
∠C = 2x + 1
∠C = 2 * 29 + 1
∠C = 58 + 1
∠C = 59°
