Oh god- i need a tad bit of help! Multiply 1 over 3 multiplied by 1 over 5.
A) negative 1 over 10
B) negative 1 over 15
C) 1 over 15
D) 1 over 10

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