Simplify the expression: 9 x + 4 y minus 7 x + 2 y.
a. 2x2 + 6y2
b. 2x + 6y
c. 8xy
d. 8x2y2

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