To simplify the expression \((7^3)^9\) using the Power Rule of Exponents, which states that \((a^m)^n = a^{m \cdot n}\), we can proceed as follows:
\[ (7^3)^9 = 7^{3 \cdot 9} = 7^{27} \]
So the simplified expression is \(7^{27}\).
Therefore, the correct response is:
7 to the 27th power