A cylindrical riser is to be designed for a sand casting mold. The length of the cylinder is to be 1.25 times its diameter. The casting is a square plate, each side = 10 in and thickness = 0.75 in. If the metal is cast iron, and the mold constant = 16.0 min/in² in Chvorinov's rule, determine the dimensions of the riser so that it will take 30% longer for the riser to solidify.