Istuck on this question someone plz

With math question will mark brainliest question in the pic.

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

Hurrya vegetable garden and a surrounding path are shaped like a square that together are 11ft wide. the path is 2ft wide if one bag of gravel covers 9 square feet how many bags are needed to cover the path