In order to solve vertical subtraction, we follow these rules:
First rule - write the problem in the correct order!
Ones digits under ones digits, tens digits under tens digits, and so on.
Second rule - when the upper digit is smaller than the lower digit - we borrow from the next digit.
Third rule - when you need to borrow from a , you cannot borrow directly from it. Instead, keep moving left through any consecutive zeros until you find a non-zero digit. Borrow from that digit, turning all the zeros you passed through into s, and the original (where you needed to borrow) becomes .