Which list has three equivalent fractions for 2/5

a. 4/10,6/20,10/25
b. 4/10,6/15,8/20
c.6/15,8/16,10/25
d.6/15,8/20,12/25

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