Answer: C. 4 hours
Explanation: You first measure how long 1/5 of an hour is in which is 12 minutes. You then multiply 12 by 20 because it takes 12 minutes to get 1/20 of the lawn watered. Your answer now should be 240. Finally, divide that number by 60 because you are measuring time in hours. Your final answer should be 4 hours.