To multiply the numbers in scientific notation, you can follow these steps:
- Multiply the coefficients: \( 7.98 \times 5 = 39.9 \)
- Add the exponents: \( -5 + -5 = -10 \)
Now, combine the results:
\[ 39.9 \times 10^{-10} \]
Next, you should express \( 39.9 \) in proper scientific notation. Since \( 39.9 \) is not between 1 and 10, we can write it as:
\[ 3.99 \times 10^1 \]
Now, we combine this with the \( 10^{-10} \):
\[ 3.99 \times 10^1 \times 10^{-10} = 3.99 \times 10^{-9} \]
So, the final result is:
\[ \boxed{3.99 \times 10^{-9}} \]