PE fund Red Llama buys a company $($with no existing debt or cash$)$ for $$500$ million, at a purchase EBITDA multiple of $10\mathrm{.}0$x$.$ Considering the financing, they figure they need to keep an interest coverage ratio of $1\mathrm{.}8$ post buyout. At that level the cost of debt is $7\mathrm{.}4\%.$ They borrow up to their debt capacity. At the end of the $3-$year period, they sell the company at an exit EBITDA multiple of $12\mathrm{.}0$x$.$ However, EBITDA has not changed at all. Capital expenditure and working capital investment are minimal and there is no dividend payment. All free cash flows are used to pay down debt. As a result, PE fund has paid off $$60$ million worth of debt during the $3-$year period.

Calculate Maximum Interest Capacity:

a$.$

$18\mathrm{.}63$

b$.$

$39\mathrm{.}21$

c$.$

$27\mathrm{.}78$

d$.$

$90$