How many Sundays are there from the date on the first leaf to the date on the second leaf, both days included?

2027 is an ordinary year starting on Friday, so only Friday occurs 53 times: 52 Sundays. 2028 is a leap year starting on Saturday, so Saturday and Sunday occur 53 times: 53 Sundays (31 December 2028 is itself a Sunday). Total 52 + 53 = 105. (104 assumes 52 in each year.)