How do I calculate confidence level or interval?

I have this data for exam grades in English Literature:

2019: the numbers achieving (A*, A, B, C, D, E) are (1, 5, 4, 7, 2, 0, 0)

2018: the numbers achieving (A*, A, B, C, D, E) are (2, 4, 3, 7, 0, 1, 0)

2017: the numbers achieving (A*, A, B, C, D, E) are (6, 5, 3, 4, 2, 0, 0)

Suppose someone says, "In 2020, if we have 20 students, the percentage getting A* will be between 10% and 20%", how do I calculate the confidence level of that statement? Alternatively, how do I calculate the 80% confidence interval?