What is the slope of the line that passes through the points (10,5) and (15,20)

What is the value of x in the this question ?

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

The functions f(x) and g(x) are shown in the graph f(x)=x^2 what is g(x) ?