21. Length of tape required to cover the edges of a semicircular disc of radius 10 cm is
(a) 62.8 cm
(b) 51.4 cm
(c) 31.4 cm
(d) 15.7 cm
Perimeter of semicircle = \( \pi r + 2r = 3.14 \times 10 + 20 = 51.4 \, cm \).