please tolong jawab no b,c,d,e,

b. K= 1/2 × π × d = 1/2 × 3,14 × 20 = 1/2 × 62,8 = 31,4
L=1/2 × π × r × r= 1/2 × 3,14 ×10 × 10= 1/2 × 314= 157