DG, DM, DS, DT GD, GM, GS, GT MD, MG, MS, MT, SD, SG, SM, ST, TD, TG, TM, TS. Those are all the possible combinations using each letter only once in each set.
Since 2 is least, we can put that at the end. That leaves us with 2 18/25 and 2 12/16. Since 12/16 is greater, we will put that as the greatest. 2 18/25 is in the middle. Hope this helps!