To add the numbers \( 8.8 \times 10^7 \) and \( 3.1 \times 10^8 \), we first need to express them with the same exponent.
We can convert \( 8.8 \times 10^7 \) to the same exponent as \( 3.1 \times 10^8 \):
\[ 8.8 \times 10^7 = 0.88 \times 10^8 \]
Now we can add the two expressions:
\[ 0.88 \times 10^8 + 3.1 \times 10^8 = (0.88 + 3.1) \times 10^8 = 3.98 \times 10^8 \]
Thus, the answer in scientific notation is:
\[ \boxed{3.98 \times 10^8} \]