Sure, I can help you simplify the expression using the Power Rule of Exponents.
The Power Rule states that when you have an exponent raised to another exponent, you can multiply the exponents together. In this case, we have (73^4)^5, so we can multiply the exponents 4 and 5 to simplify the expression.
(73^4)^5 = 73^(4 * 5)
Now, we can multiply the exponents:
73^(4 * 5) = 73^20
Therefore, the simplified expression is 73^20.