Beulah, the good news is that your digits 1,3 and 4 are correct. So you probably don't need to rework previous answers. (42) is 15659 and (20) is 1786, therefore (21) < 13873.
Digit sums for (21) + (31) = (12) + (40). I make that (21) + 10 = 23 + 9.
So digit sum(21) = 22.
You already have a total of 10 for digits 1,3 and 4, So digits 2 & 5 must total 12. Only one arrangement, that is values 3 and 9 for digits 2 & 5 respectively, satisfies (21) < 13873