Plz 99 pts and will choose a brianyest there are more than 1 screen shot dont answer if u cant see them all

Empty box + box + empty box fill in the box is equal to 30 how

Ineed to know the answer to this algebra question.

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