Explanation:
it is an equal distribution : every data value has the same frequency of occurrence - 1/14 of all students.
so, 1/14 of her students practice 1 hour, 2 hours, 3 hours, ..., 14 hours.
every hour is represented not just by a line but by a bar one unit thick (going from the hour value to the begin of the next hour value).
so, we have 14 different values for weekly practicing.
and, as mentioned, precisely 1/14 of her students practice one of these hour values for each of these values.
so, the orange shaded part stands for the students that practice 6 or 7 hours per week.
"between 6 and 8 hours" is only correct, if that excludes the end (8 hour) value. otherwise "between 6 and 7 hours" is correct.
bottom line : this is only a 2- hour interval (6 and 7 hours practicing).
and so, this interval stands for 2/14 of all her students.
2/14 = 1/7 = 0.142857143... ≈ 14%
and now the other concern I have : what is the shaded part ? if it is not the orange but the blueish part, then we are talking about all the students except for those that practice 6 or 7 hours per week.
and that would be then 12/14 = 6/7 = 0.857142857... ≈
≈ 86% of her students.