PLEASE HELP.
20 POINTS

Write numerical coefficient of y² in the expression 2x² - 15xy – 7y²

Which is greater, 7 p 5 or 7 c 5? 7p5 7c5

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