To multiply the two numbers in scientific notation, you multiply the coefficients and add the exponents.
Given:
\[ (9 \times 10^4) \cdot (8 \times 10^9) \]
Step 1: Multiply the coefficients (9 and 8).
\[ 9 \times 8 = 72 \]
Step 2: Add the exponents (4 and 9).
\[ 4 + 9 = 13 \]
Step 3: Combine the results into scientific notation.
The result is:
\[ 72 \times 10^{13} \]
However, since scientific notation typically has a coefficient between 1 and 10, we need to convert 72 into proper scientific notation:
\[ 72 = 7.2 \times 10^1 \]
Thus, we rewrite our answer:
\[ 7.2 \times 10^1 \times 10^{13} \]
Now, combine the powers of 10:
\[ 7.2 \times 10^{1 + 13} = 7.2 \times 10^{14} \]
The final answer in scientific notation is:
\[ \boxed{7.2 \times 10^{14}} \]