1. Start subtracting from the ones place.
   
2. If the subtrahend is lesser than minuend then we borrow 1 from tens place.
3. If the subtrahend is lesser than minuend in tens place then we borrow 1 from hundreds place.
4. If the subtrahend is lesser than minuend in hundreds place then we borrow 1 from thousands place.

Example 1:

Question	Step 1	Step 2	Step 3	Step 4

1. Start from ones place 5 minus 5 is 0.
2. In the tens place, 3 minus 2 is 1.
3. In the hundreds place 4 minus 1 is 3.
4. In thousands place, 9 minus 5 is 4.

Example 2:

1. Start from ones place 8 minus 6 is 2.
2. In the tens place, 9 minus 9 is 0.
3. In the hundreds place 9 minus 8 is 1.
4. In thousands place, 4 minus 2 is 2.

1. Start from ones place 7 minus 2 is 5.
2. In the tens place 3 is less than 8, so 1 is borrowed from 0 which has borrowed 1 from 3. So the result in tens place is 13 minus 8 which is 5.
3. In the hundreds place 0 becomes 9, the result is 3.
4. In thousands place, 3 becomes 2 and the result is 1.