Help last 3 questions thanks so much!

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

What is the 9th term in the geometric sequence described by this explicit formula? an=-6. (2)(n-1) apex

Let f(x) = 5/x and g(x)=2x2+5x. what two numbers are not in the domain of f o g