If 10 is the average then the sum of the 5 integers=5×10=50.
If 4 of the chosen integers are allowed to be the same, then the four could be 1s, the 5th integer would then be 50-4=46. That’s the largest possible integer making the set 1, 1, 1, 1, 46, average 10.
If none of the integers can be the same, then the lowest set for 4 of the integers must be 1, 2, 3, 4, which add up to 10, so the 5th integer is 50-10=40. That’s the largest possible if all the integers are different.