A man riding a bicycle. completes one lap of a square field along its perimeter at the speed of 43.2 km/hr in 1 minute 20 seconds. What is the area of the field ?

To convert km/hr to m/sec multiply the speed with $$\frac{5}{18}$$.
39.6 km/hr = $$\frac{43.2\times 5}{18}$$ = 12 m/sec
The man covers the entire distance in 1 minute and 20 seconds which is equal to 80 seconds.
Distance=Speed $$\times$$ Time = 12 $$\times$$ 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.