I think i need to use the IF function here, but i'm not sure. Here's what
I'm trying to do.

If cell A1 and B1 ARE coded with "P" or "PD" assign a value of "1" in C1.
If cell A1 IS NOT coded with "P" or "PD" and B1 IS coded with "P" or "PD"
assign a value of "2" in C1.
If cell A1 IS coded with "P" or "PD" and B1 IS NOT coded with "P" or "PD"
assign a value of "3" in C1.
If cell A1 and B1 ARE NOT coded with "P" or "PD" assign a value of "4" in C1.

I hope someone can help. Example spreadsheet is below:

Column A Column B Column C
P PD
L P
PD M
T T