To simplify the expression \((73^4)^5\) using the Power Rule of Exponents, you apply the rule that states \((a^m)^n = a^{m \cdot n}\).
So for your expression:
\[ (73^4)^5 = 73^{4 \cdot 5} \]
Now calculate \(4 \cdot 5\):
\[ 4 \cdot 5 = 20 \]
Thus, we have:
\[ (73^4)^5 = 73^{20} \]
So the simplified expression is:
\[ 73^{20} \]