Convert Letter Grade to Quality points

[ExcelHel]

I need help converting letter grades to quality points. In E1 I have "grades" and then from E2-E21 I have letter grades ranging from A to D. In F1 I have "credits" and in F2-F21 I have a number ranging from 1 to 4. I put "Quality Points" in G1. How do I make my letter grades equal numbers A=4, B=3,C=2,D=1, and then how do I get it to multiply that by the credits. So if my Letter grade in E2 is an A and its worth 3 credits(F2) how do I make excel calculate that G2 should equal 12. Thanks a ton.

 

[ExcelHel]

And for the record I am brand new to excel so try to dumb it down as much as possible.

 

[Andrew Poulsom]

In G2 copied down:

=LOOKUP(E2,{"A","B","C","D"},{4,3,2,1})*F2