37. The area of a semicircle of radius 4r is
(a) 8πr²
(b) 4πr²
(c) 12πr²
(d) 2πr²
Area of semicircle = \( \tfrac{1}{2} \pi (4r)^2 = \tfrac{1}{2} \pi \times 16r^2 = 8πr² \).