In mathematical subtraction, if there are not enough digits, you can borrow one from ten digits. In this case, you can subtract 1 from the ten-digit number and add 10 to the one-digit number. For example, 6-3=3, considering that the unit of 6 is not enough to subtract 3, then we can subtract 1 from the number 5 in its decimal digits to become 4, and then add 10 to its unit to become 14. This can make 6-3=3.

If ten people don't borrow time, then we will solve the problem by filling in zeros. For example, 7-8= at this time, the single digit of 7 is not enough to subtract 8. Considering that its ten digits are also 0, we should add a zero before 7, rewrite it as 07, and then 07-8=-1.