ACCORDING to the rate of electricity charge, the minimum charge up to 20 unit is Rs 80 and the cost per unit from 21 units to 250 units is Rs 7.30. How many units were consumed by Rs 1248? ​

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