Assume that a not-for-profit company has $20 million of long-term tax-exempt debt with an interest rate of 6.0%. The organization has $3 million of unrestricted net assets, with an estimated cost of capital of 7.5%, and $9 million in an endowment with an estimated 5.0% return on assets (cost of capital). What is its weighted average cost of capital?

Show all work and provide an explanation.