Originally Posted by
ArcSine
Your cost of equity is correct; your cost of debt is not.
The cost of Jones' debt is simply the interest rate that corresponds to the 600,000 loan amount being exactly amortized with 10 annual payments of 100K each.
For example, had Jones borrowed the 600K at (say) 14% with a 10-year payback, their annual payment would be 115,028. If they had instead borrowed at (say) 9%, their annual payment would be 93,492.
Since their annual payment is actually 100K, then right away my examples tell you that the cost of the debt must lie somewhere between 14% and 9%.
To find the actual rate (and hence the cost of the debt), there are multiple approaches. You could use a "present value of an annuity" table; you could set up the "present value of an annuity" formula in a calculator and use trial-and-error iterations to narrow in on the answer; you could set up an amortization schedule in a spreadsheet---with an initial loan amount of 600K and 10 payments of 100K---and then tinker with the interest rate until the loan is exactly paid off following the tenth payment. Without knowing which method you've been given in your book or class, I can't advise on the specifics, but maybe the foregoing will give you enough to take the baton and run with it.