The range measures the spread of the dataset by calculating the difference between the largest and the smallest element. In your case, marks range from 6 to 10, so the range is 10-6=4.
How many students
The frequency tells you how many students got each mark. So, we know that 5 students got a mark of 6, 4 students got a mark of 7, 7 students got a mark of 8, 10 students got a mark of 9, 4 students got a mark of 10.
This implies that, in total, we have
students.
Mean
The mean is given by the sum of the marks, divided by the number of students. We already observed how many students got each mark, so the sum of all marks will be a weighted sum, where each mark counts once per student:
Now we divide this sum by the number of students to get
So, the average mark is about 8.