The PDF you posted shows classes2.txt to be a file in your home directory, which commonly can be represented by a tilde (~).
So try changing
filename gpa "/folders/myfolders/classes2.txt";
to
filename gpa "~/classes2.txt";
Your home directory, in absolute terms, is probably something like /home/odaws01-usw2, which (if correct) would require you to use
filename gpa "/home/odaws01-usw2/classes2.txt";
It's a lot easier to use the ~ symbol.