I just learnt perms and combs over the last few days so this might be wrong (someone correct me if I'm wrong) but here's how I'd do it:
We want the vowels in alphabetical order. Given any two spaces in this six letter word, we can obviously arrange the vowels alphabetically in one way (put the a in the first spot and the e in the second). We can choose two spaces out of 6 in 6C2 ways. Now we can arrange the other four letters in whatever way we want so the total arrangements are:
You can also arrange the two vowels in alphabetical order first. This will always be the "total letters minus one" triangular number. There are 6 letters, so we take the 5th triangular number, ie 15.
Now the other 4 consonants can be arranged in 4! ways = 24 ways.