Final answer:
The amount of the porters' investment interest expense deduction for the year is $183 million.
Step-by-step explanation:
The amount of the porters' investment interest expense deduction for the year is $183 million.
This is calculated based on the given information that the interest rate is 9% and the firm can capture a 5% return to society. The firm would invest as if its effective rate of return is 4% which leads to an investment of $183 million.