Given,
The data of the length of the fishes is,
class interval frequency
 2 - 5 10
 6 - 9 12
 10 - 13 6
 14 - 17 7
Required
The mean length of the fishes.
Taking the class interval as,
class interval x frequency
 1.5 - 5.5 3.5 10
 5.5 - 9.5 7.5 12
 9.5 - 13.5 11.5 6
 13.5 - 17.5 15.5 7
Mean length of the fishes is,

Hence, the mean length of the fishes is 8.64 inches approximately.