You have a fox, a chicken, and a bag of chicken feed, and must take them all to the other side of a river. You have a boat but can only take one thing across at a time. You cannot leave the chicken with the fox, nor the chicken with the bag of chicken feed. Answer this riddle

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