A man can do a piece of work in 20 days. i. how much work does he do in 1 day
ii. how much work does he do in 5 days
iii. if he leaves the work after 10 days, how much work is left to do?

pls pl help​

Apinhole camera is made out of a light-tight box with a piece of film attached to one side and pinhole on the opposite side. the optimum diameter d(in millimeters) of the pinhole can be modeled by d=1.9[ (5.5 x 10^-4) l) ] ^1/2, where l is the length of the camera box (in millimeters). what is the optimum diameter for a pinhole camera if the camera box has a length of 10 centimeters