To add the two numbers \( 8.8 \times 10^7 \) and \( 3.1 \times 10^8 \), we first convert them to the same power of ten.
The term \( 3.1 \times 10^8 \) can be expressed as \( 31.0 \times 10^7 \) (since \( 10^8 = 10 \times 10^7 \)).
Now we can add:
\[ 8.8 \times 10^7 + 31.0 \times 10^7 = (8.8 + 31.0) \times 10^7 \]
\[ 39.8 \times 10^7 \]
Next, we convert \( 39.8 \times 10^7 \) into standard scientific notation. We can express \( 39.8 \) as \( 3.98 \times 10^1 \). Thus:
\[ 39.8 \times 10^7 = 3.98 \times 10^1 \times 10^7 = 3.98 \times 10^{1+7} = 3.98 \times 10^8 \]
Therefore, the final answer in scientific notation is:
\[ \boxed{3.98 \times 10^8} \]