B it is ,
you don't need to complete calculation if you see there is some cord which is connecting the two discs and and two sectors are left free without cord .
calculate disc 1 = 270/360 * 2* pi*80
cl . disc 2 - 270/360 *2 * pi* 60
= 90pi + 120 pi = 210 pi + the extra length
if look at the choice there is only once choice which is 210 oi + extra B
so the rest you need not calculate .
let me know if their is any flaw in my reasoning .
---- Hero never chooses Destiny
Destiny chooses Him ......