The villagers build underground water canal to fill the well, in which water flow with 2m/sec & its width is 30cm & length 80cm. How much time will it take to fill one well of radius 3cm & 21m deep

2 answers

All subjects? Looks like MATH to me!
EXPRESS all lengths in METERS, not cm
for example I do not believe your well is radius of 3 cm

Volume of well = V = pi r^2 * 21

Q = flow rate
Q = width * depth * 2 m/s

V = flow rate Q * time t