Problem: a certain rectangular crate measures 12 feet by 16 feet by 18 feet . a cylindrical gas tank is to be made for shipment in the crate and will stand upright when the crate is placed on one of its six faces . what should the radius of the tank be if it is to be of the largest possible volume ? 
Options: ['a ) 4', 'b ) 5', 'c ) 6', 'd ) 8', 'e ) 10']
d