In a triangle ABC, ∠ABC = 75° and ∠ACB = ^c4, the circular measure of ∠BAC is?

Answer: Option B

$$\begin{array}{rl}& \frac{{\pi }^c}{4}\text{ = }\frac{{180}^{\circ }}{4}\text{ = }45^{\circ }\\ & \angle \text{BAC}=180^{\circ }-75^{\circ }-45^{\circ }=60^{\circ }\\ & 180^{\circ }\to \pi \\ & 1^{\circ }\to \frac{\pi }{{180}^{\circ }}\\ & 60^{\circ }\to \frac{\pi }{{180}^{\circ }}\times 60^{\circ }=\frac{\pi }{3}\text{ radian}\end{array}$$