Create PDF to calculate GPA

I created a transcript template.  How can I make it calculate the Grade points Earned.

If I input 6 in the credit hours attempted column and an "A" in the grade column, I would like for it to automatically calculate 24 in the grade points earned column.  How would I go about doing this?

The grades would be:

A = 4

B = 3

C = 2

D = 1

F = 0

Thank you!