Respuesta :

(360/10)/2 = 18°

Cos(18)=a/r=a/5 ---> a=4.8

Tan(18)=o/a=o/4,8 ---> o=1.6

Area = 1/2 * 4.8 * 1.6 * 20 = 76.8 

The right answer is A, i have just rounded up, so i didn't get is precise.