Im kinda new to SQL Server.

• Dataset: Fact_Centre_Txn
  Centre_Id Cust_Id Visit_Date Transaction_Id Transaction_Amt
  N02 2 2022-04-02 16:13:00.000 1 209
  N02 14 2022-04-28 13:22:00.000 2 187
  N01 8 2022-02-14 00:12:00.000 3 15
  E01 6 2022-02-11 16:36:00.000 4 111
  N01 1 2022-03-10 03:51:00.000 5 -298
  W01 10 2022-03-04 03:05:00.000 6 -401
  W01 4 2022-03-09 22:39:00.000 7 65
  N01 5 2022-02-13 23:14:00.000 8 44
  S02 15 2022-05-02 15:36:00.000 9 -30
  S02 15 2022-02-13 05:28:00.000 10 -27
  …and so on

• Requirement: Display the average number of days between a customer’s last and second to the last transaction

• What I got: Figured out maybe I can use ROW_NUMBER and select the Visit_Date with row_num 2 and 3 (PARTITION BY Cust_Id and ORDER BY Visit_Date DESC) corresponding with the last date and second date to the last transaction. Not quite figuring out what to do next with that idea

All helps are appreciated!