Please help me (￣ ‘i ￣;)

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

In which direction does the left side of the graph of this function point? f(x) = 3x3 - x2 + 4x - 2

Which of the following scenarios demonstrates an exponential decay