Example:

The first user license costs $80.00. Each additional user, for the next 4 users costs $24.00. After that, the next 5 users cost $12.00, and the next 15 users cost $6.00 and so on.

Say you have 30 students. You would pay a 1 time license fee for 30 students:

$80.00
$24.00 x 4
$12.00 x 5
$6.00 x 15
$3.00 x 5

Total: $341.00

Later, you want to add 3 more students. $3.00 x 3 = $9.00. So you pay a 1 time license fee of $9.00 for 3 additional students.