Use addition:
765 + 98:
Line up our numbers vertically:
7 | 6 | 5 | |
+ | 9 | 8 |
7 | 6 | 5 | |
+ | 9 | 8 | 3 |
Column 1: 5 + 8 = 13
Since 13 > 9, we take the right digit = 3.
Carry the 1 for Column 2
1 | |||
7 | 6 | 5 | |
+ | 9 | 8 | 6 | 3 |
Column 2: Carry the 1 from Column 1
1 + 6 + 9 = 16
Since 16 > 9, we take the right digit = 6.
Carry the 1 for Column 3
1 | 1 | ||
7 | 6 | 5 | |
+ | 9 | 8 | 8 | 6 | 3 |
Column 3: Carry the 1 from Column 2
1 + 7 + 0 = 8