To simplify the expression \((73^4)^5\) using the Power Rule of Exponents, we apply the rule, which states that \((a^m)^n = a^{m \cdot n}\).
For the expression \((73^4)^5\):
- Identify the base \(a = 73\).
- Identify the exponents \(m = 4\) and \(n = 5\).
Now, apply the Power Rule:
\[ (73^4)^5 = 73^{4 \cdot 5} = 73^{20} \]
Therefore, the simplified expression is:
\[ 73^{20} \]