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
(In reply to Both at once?
by Brian Smith)
I found 10 solutions for solving both alphametics simultaneously (x is the unused digit):
To minimize the sum of the used digits, the unused digit must be as large as possible. This leaves the 7th solution as the solution with the smallest sum of digits used. 461+359=820 46+13=59