Hi!
It is really important to find as many different solutions as possible for a problem. The reason is, that sometimes a certain solution won’t work depending on the situation. So you need to have alternatives.
For question 80 I offered two possibilities, one with user-variables and one with a subquery. Are there more?
[Just for fun]
Another solution for Q80 is using a helper table and a join.
The helper table is created with the correct sort order and a surrogate key is added to support the join between the rows.