A coffee shop tracks daily sales of a new pastry. The average number of pastries sold per day over the first 6 days after launch is 45, and over the first 7 days is 48. On the 8th day, the shop sells 7 pastries more than on the 7th day. The average number of pastries sold per day from the 2nd day to the 8th day is 52. The number of pastries sold on the 1st day after launch is: