Fill in the blanks. See picture and give answers please as quickly as possible.

John bought 5 lemons and used 2 of them for a salad how much did he use for.a salad . he used % of the lemons.

I’m stuck on this equation, anyone got the answer?

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