=IF(AND($F11="",$G11=""),"",IF(AND($F11="?",$G11="?"),"",IF(AND($F11=0,$G11=0),0,IF(OR($F11>0,$G11>0),(E11*F11)+(E11*G11/2)))))

Can anyone tell me what the "" and the "?" in the above formula mean? and what is the "" between the IF statements?

Thanks for your help!

Brian