Excel Forumla help (IF formula)

Hello,

I need some help, I just can't figure the IF formula out. On my Excel 2007 spreadsheet, I am trying to figure out if I put the letter grade of a B in one column and then in another separate column it automatically produces a 3. Also, I need each column to be flexible so that if I get an A in on course, then the corresponding column next to it will produce a 4 in it. I am trying to make a spreadsheet to keep track of my ongoing grades and I am stuck on this step. Thanks for the help in advance.