Math pls! question 1: 3.6/y = 1.2/2 then y = ? question 2: 5/25 = m/125 then m = ? question 3: n: 1/2 as 6: 1 n = ?

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