The diameter of an optimum cylindrical riser (height = diameter) attached to the side of a steel plate casting having dimensions of 25 cm x 12.5 cm x 5 cm, by assuming that volumetric shrinkage of solidification is 3% for steel and that the volume of the riser is 3 times that by the shrinkage considerations alone, will be:

• A. 8.32 cm
• B. 7.26 cm
• C. 3.24 cm
• D. 5.64 cm