Jack delivered 90 circulars in 20 minutes. At this rate, how long will it take him to deliver 135 circulars?

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

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What is the circumference of a circle with an area of 50.24 cm²?