the area of a rectangular field is 3584m sq and its lenght is 64m. A boy runs around the field at the rate of 6 km/h. how long will he take to go 5 times around it?

Length of rectangular field = 64 m
Area of rectangular field = 3584 ${\mathrm{m}}^2$
So breadth of rectangular field = $\frac{3584}{64} = 56$ m
Then, Perimeter of rectangular field = $2\left(64+56\right) = 240 \mathrm{m}$
Now a boy is running 5 times around the field. So total distance covered by a boy = $240\times 5 = 1200$ m
Speed = 6km/h = $\frac{6\times 1000}{60\times 60} = \frac{5}{3}$m/s
So time taken by boy to cover the total distance = $\frac{1200}{{\displaystyle \frac{5}{3}}}=\frac{1200\times 3}{5} = 720$
therefore time taken by boy is 720 seconds.