Step-by-step explanation:

Formula

Circumference\ of\ a\ circle = 2\pi rCircumference of a circle=2πr

Where r is the radius of the circle .

Speed = \FRAC{Distance}{Time}Speed=TimeDistance

As given

A man take to MAKE a of a circular field of radius 21 m.cycling at the speed of 8km/h .

Put all the values in the formula

\pi =\frac{22}{7}π=722

Circumference\ of\ a\ circle = 2\times \frac{22}{7}\times 21Circumference of a circle=2×722×21

Circumference\ of\ a\ circle = 2\times 22\times 3Circumference of a circle=2×22×3

Circumference\ of\ a\ circle = 132\ mCircumference of a circle=132 m

As 1 km = 1000 m

1\ m = \frac{1}{1000}\ km1 m=10001 km

Now convert 132m into km .

132\ m = \frac{132}{1000}\ km132 m=1000132 km

                  = 0.132 km

I.e

Distance = 0.132 km

Speed = 8 km / h

Put all the values in the formula

8 = \frac{0.132}{Time}8=Time0.132

Time= \frac{0.132}{8}Time=80.132

Time = 0.0165 hr

As

1 hour = 3600 second

Now convert  0.0165 hr into seconds .

0.0165 hour = 0.0165 × 3600

                      = 59.4 seconds

Therefore the time taken by the man who cycling at the speed of 8km/h on circular field is 59.4 seconds .

hope this help you.

mark as best as your wish.