16. The diagram shows a triangle with edges of length 3,4 and 6 . A circle of radius 1 is drawn at each vertex of the triangle. What is the total shaded area?
A $2 \pi$
B $\frac{9 \pi}{4}$
C $\frac{5 \pi}{2}$
D $\frac{11 \pi}{4}$
E $3 \pi$
16. C The sum of the interior angles of a triangle is $180^{\circ}$. So the three unshaded sectors inside the triangle have a total area equal to one half of the area of a circle of radius 1 . Therefore the total shaded area is equal to the area of two and a half circles of radius 1 , so the required area equals $\frac{5}{2} \times \pi \times 1^{2}=\frac{5 \pi}{2}$.