What is the difference (2x-3) - (x- 1) x-4 x-2 x+2 x+4

How do i do this? i don’t understand

If y varies directly as x2 and y=6 when x=6, find the constant of variation.

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