If the US government decides to give you $1 for today, and double it after that everyday. Like $2 tomorrow, $4, $8, etc How much money will you get after 30 days?
Think and come up with a rule.

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