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.
The answer or number that you are looking for is -6.4. You can get this by dividing 3 by 5 which is equal to 0.6. Next you would subtract 7 to reverse the act of having added it. This will give you -6.4 which is what you are looking for.
