Ahmed is interested in how many gallons of gasoline his neighbors use per week. He collected the following data from about one third of his neighbors, selected at random.

9used between 1 and 20 gallons, 5used between 21 and 40 gallons, 2used between 41 and 60gallons, 2used between 61and 80gallons, and 2used between 81 to100

Calculate the mean gallons of gasoline used per week. Keep all intermediate steps to four decimals then enter your answer to two decimals.