Hello excel brains trust..

i need to show growth of student learning based on the student reading levels from Term 2 2019, to the reading level they are at term 2 2020 (1 year apart).

For example, if a student was on reading level 3 in 2019, and by the same time in 2020 they are now on reading level 14, how do i show that growth as a % and what is the formula so i can apply to all students reading levels.
FYI - Students can get to a top of level 30. This is their highest level.

PLEASE HELP!