Classification Estimator with a Function-Help

[auspackuk]

Average Mark Classification
>=70 1st
60 -69 2.1
50-59 2.2
40-59 3rd
<39 Unclassified

I want to write a program to estimate the degree of classification from an average mark. For example, an average mark of 55% shd give 2.2 classification.


I need to add a Function that shd take a single parameter value for the average mark, and return the calssification average.

Here are my design: I am new to this and need code solution to this please.