4. (10 points) Xiao Ming bought 4 apples, 6 pears, and 8 peaches, while Xiao Hong bought 5 apples, 7 pears, and 6 peaches. In the following 18 days, each of them eats one fruit per day, with three days both eating apples; two days both eating pears, and three days one eating an apple and the other eating a pear. Therefore, there are $\qquad$ days both eating peaches.
【Answer】Solution: (1) For three days, both ate apples, and for two days, both ate pears. After 5 days, Xiao Ming has 1 apple and 4 pears left, while Xiao Hong has 2 apples and 5 pears left;
(2) For three days, one person ate apples while the other ate pears, so when Xiao Ming ate the remaining 1 apple, Xiao Hong ate pears; when Xiao Hong ate the remaining 2 apples, Xiao Ming ate pears;
(3) When Xiao Ming ate the remaining 2 pears, Xiao Hong could only eat peaches; when Xiao Hong ate the remaining 4 pears, Xiao Ming could only eat peaches;
(4) At this point, both have 4 peaches left, so they ate peaches together for 4 days.
Answer: There are 4 days when both ate peaches.
Answer: 4.