Use addition:
375 + 43:
Line up our numbers vertically:
3 | 7 | 5 | |
+ | 4 | 3 |
3 | 7 | 5 | |
+ | 4 | 3 | 8 |
Column 1: 5 + 3 = 8
3 | 7 | 5 | |
+ | 4 | 3 | 1 | 8 |
Column 2: 7 + 4 = 11
Since 11 > 9, we take the right digit = 1.
Carry the 1 for Column 3
1 | |||
3 | 7 | 5 | |
+ | 4 | 3 | 4 | 1 | 8 |
Column 3: Carry the 1 from Column 2
1 + 3 + 0 = 4