(* pp.440--,#24,36,46,51 *)
(* 24 *)
rads=5Pi/18
degs = rads*360/(2Pi)

(* 36 -- no, difference isn't a multiple of 2Pi *)  
Simplify[32Pi/3-11Pi/3]

(* 46 *)
rads=-7Pi/3
rads+2Pi
rads+4Pi

(* 51 *)
radius=5
degs=360-140
rads=degs*2Pi/360
s=rads*radius