A small library tracks the daily number of book check-outs after launching a new lending programme. The average number of books checked out per day over the first 6 days is 40, and over the first 7 days is 44. On the 8th day, 9 fewer books were checked out than on the 7th day. The average number of check-outs per day from the 2nd day to the 8th day works out to 48. The number of books checked out on the 1st day of the lending programme was: