Ανά didn't appear in the hints, and this is a new word to me. (I have a screenshot, but I don't know how to show it here.)
Same here, Aug.9.2020
Wouldn't "Τρια τη εβδομαδα" be acceptable?
Your translation is almost correct. One never says "τη εβδομάδα" but "τη βδομάδα" (you have to omit the "ε"). It's the same as "μέρα" and "ημέρα" (= day). :-)
Ευχαριστω βρε Παναγιωτη. Να'σε καλα.
What is wrong with using για instead of ανά?
Τρία για βδομάδα just makes no sense in Greek, τρία για μία βδομάδα means "three for a week" (in the sense of: How many shirts do you need for the trip? I need three for a week). Three a week can be Τρία την βδομάδα or τρία ανά βδομάδα.