Answer:
15%
Step-by-step explanation:
Calculation to determine would be the break-even interest rate (BEIR)
Using this formula
Break-even interest rate (BEIR)= After tax IRR on total investment / (1- Tax rate)
Let plug in the formula
Break-even interest rate (BEIR)=9% / (1-0.40)
Break-even interest rate (BEIR)=9%/0.60
Break-even interest rate (BEIR)= 15%
Therefore would be the break-even interest rate (BEIR), at which the use of leverage is neither favorable nor unfavorable is 15%