We are asked to determine the total number of students in a school. To do that we need to add the number of students in each of the year classes. Beginning with the 9th class we have:

Now, the number of students in the 10th year class is 20% more, this means:

Now, the number of students in the 11th year class is:

The 12th year class is:

Now we add all the students in each class:

Therefore, there are about 1610 students in Townsend High School.