4.2x - 1.4y =2.1 s someone plz me solve for y

The quadratic function h(t)=-16.1t^2+150 choose the graph representation

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 missing value in the proportion 4/5 = x/30