Use subtraction:
1797 - 1732:
Line up our numbers vertically:
1 | 7 | 9 | 7 | |
_ | 1 | 7 | 3 | 2 |
1 | 7 | 9 | 7 | |
_ | 1 | 7 | 3 | 2 | 5 |
Column 1: 7 - 2 = 5
1 | 7 | 9 | 7 | |
_ | 1 | 7 | 3 | 2 | 6 | 5 |
Column 2: 9 - 3 = 6
1 | 7 | 9 | 7 | |
_ | 1 | 7 | 3 | 2 | 0 | 6 | 5 |
Column 3: 7 - 7 = 0
1 | 7 | 9 | 7 | |
_ | 1 | 7 | 3 | 2 | 0 | 0 | 6 | 5 |
Column 4: 1 - 1 = 0