The highway mileage (in miles per gallon) for 30 small cars

Mileage (in miles per gallon)                        Frequency

29 – 33 …………………………………………..     11

34 –38 …………………………………………..      12

39 – 43 …………………………………………..      2

44 – 48 …………………………………………..      5

Approximate the mean of the frequency distribution.