i have another problem

what is the formula if i have three grades and in A1.B1 & C1. i need a final grade answer in D1. I need a formula which could result in any of the answers below related to the recorded grade

A B C D
1 P M D = Distinction

or
A B C D
1 P M X = Merit

or
A B C D
1 P x x = Pass

or
A B C D
1 x x x = Refer


hope someone can help

tomo