Question 29In the figure $\overline{PA}$ is tangent to semicircle $SAR;$ $\overline{PB}$ is tangent to semicircle $RBT;$ $SRT$ is a straight line; the arcs are indicated in the figure. Angle $APB$ is measured by: $\dfrac12(a-b)$$\dfrac12(a+b)$$(c-a)-(d-b)$$a-b$$a+b$
