Staggered tire replacement question

[Cavman]

TPMS went off on my way home and I found a metal object has basically slashed my driver side rear tire.

Have the staggered 20" setup.

I happen to have an extra set of summer tires (275 from / 315 rear) and I was wondering:

1) if I could replace just the tire that has a hole in it?

2) do I need to replace both rear tires

3) do I need to replace all 4 tires (Audi used to recommend that all tires in Quattro have the same tread wear but not sure if xDrive is the same.


Just trying to figure out what/how many tires I need to bring with me to the dealer tomorrow morning.

Any help tonight would be appreciated.

Thank you