Solution - Long subtraction

Subtract the numbers in the ones column from the top number:
8-7=1

Because the upper digit (1) in the tens column is too small to get a positive difference, borrow 1 from the digit (4) in the next number place which becomes (3) and get (11).

Subtract the numbers in the tens column from the top number:
11-2=9

Because the upper digit (3) in the hundreds column is too small to get a positive difference, borrow 1 from the digit (9) in the next number place which becomes (8) and get (13).

Subtract the numbers in the hundreds column from the top number:
13-4=9

Subtract the numbers in the thousands column from the top number:
8-2=6

Subtract the numbers in the ten thousands column from the top number:
4-2=2

Subtract the numbers in the hundred thousands column from the top number:
2-2=0

The solution is: 26,991