Problem: a ring x of diameter 16 inches is placed inside another ring y of diameter of 18 inches . how much fraction of the ring x surface is not covered by the ring y ? 
Options: ['a ) 13 / 15', 'b ) 12 / 4', 'c ) 16 / 17', 'd ) 22 / 16', 'e ) 17 / 81']
e