Will i get this right 18(1+4)

Iwill make brain if you me correctly fill this out needs due today pls and send it back to me (click the link and you will get it)

With finding limits of multi variable !

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