To convert km/hr to m/sec multiply the speed with $$frac{5}{18}$$.
39.6 km/hr = $$frac{43.2 imes 5}{18}$$ = 12 m/sec
The man covers the entire distance in 1 minute and 20 seconds which is equal to 80 seconds.
Distance=Speed $$ imes$$ Time = 12 $$ imes$$ 80 = 960 m
The perimeter of the field is 960m.
Length of one side of the field = $$frac{960}{4} = 240$$ (Since it is a square field.)
Area of the field = $$240^{2}$$ = 57600 sq. mts
Hence Option B is the correct answer.