Cell phone company charges $20 per month plus $.50 per text message. write an equation that shows how your total bill depends on the number of text messages sent

What is a graph with a never ending line called?

I’m stuck on this equation, anyone got the answer?

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