Problem: it has been raining at the rate of 5 centimeters per hour . if the rain filled a cylindrical drum with a depth of 15 centimeters , and area 300 square centimeters , how long did it take to fill the drum completely ? 
Options: ['a ) 3 hours', 'b ) 4 hours 15 minutes', 'c ) 6 hours', 'd ) 2 hours 5 minutes', 'e ) 8 hours']
a