There are several days' differences in math problems between the seventh summer and the 23rd summer.

The summer heat lasts from July 6th to July 7th or 8th in the Gregorian calendar every year, and the summer heat lasts from July 22nd or 23rd or 24th every year, so the difference is about15th day. 24 solar terms adopts the method of "fixing qi", that is, on the ecliptic with a circumference of 360 degrees (the apparent path of the sun on the celestial sphere for one year), it is divided into 24 equal parts, and every 15 is 1 equal part, so the interval between two solar terms is about 15 days.

The subtraction of natural numbers is not closed. It is closed unless the minuend is greater than the minuend. For example, 1 1 cannot subtract 26. In this case, use one of two methods.