Believe me - there are numerous solutions of the above alphametic.
I. What is the minimal possible sum of participating digits?
ii. Same question for as+df=gh
17 is the minimal possible sum.
For instance, 13 + 27 = 40
This is clearly better than using 1-6 (sums to 21), so we need a solution with a 0.
0 - 5 does not work because we need two digits that sum to 10.
0 1 2 3 4 6 Does not work. Since we need a carry, the sum of the digits must be odd.
And any other solution sums to more than 17.