Problem: a certain barrel , which is a right circular cylinder , is filled to capacity with 60 gallons of oil . the first barrel is poured into a second barrel , also a right circular cylinder , which is empty . the second barrel is twice as tall as the first barrel and has twice the diameter of the first barrel . if all of the oil in the first barrel is poured into the second barrel , how much empty capacity , in gallons , is left in the second barrel ? 
Options: ['a ) there is no empty capacity', 'b ) 100 gallons', 'c ) 300 gallons', 'd ) 420 gallons', 'e ) 840 gallons']
d