How much did Briana save by purchasing a backpack that cost $45 with a sales promotion of 20% off instead of a backpack that cost $42 with a sales promotion of 10% off?
$1.80
$3.00
$4.80
$6.90

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