SOLUTION: it takes 21 days for 21 chickens to lay 21 eggs, how many days will take 14 chickens to lay 14eggs?

That's one egg apiece, so it takes 21 days for each chickens to lay one egg
apiece.

Therefore no matter how many chickens you have, each one of them will
lay exactly one egg in 21 days.

So it's no different for the time required for 14 chickens to lay 14 eggs,
21 chickens to lay 21 eggs, or 1000 chickens to lay 1000 eggs, or just 1 chicken
to lay 1 egg.  It will always take 21 days for each chicken to lay one egg.

So the answer is 21 days.

Edwin