First off, Merry Christmas @spectrumecons!
Now, my attempt at the main puzzles (with a couple notes thereafter):
- 1
- 126, 924, 105, 816
- 61
- 138
For some reason, I came up with Australia = 62 on puzzle #3 but the other clues made sense and so there's no net effect. On puzzle #4, that "52" was bothering me but I just rolled along with it -- my answer assumes the "52" to be correct.
Australia = 62 is correct, well spotted @doughtaker. I have updated the post. I checked Question 4, 52 is fine.