a company has issued 12% redeemable debt with 5 years to redemption. redemption is at par. the current market value of the debt is 107.59. the tax rate is 30%. wat is required return by the debt providers?

it's answers is 10.63.

but i don't know how to decide two rates to compute it? is it all judgement?

irr= a+(A/A-B)*b-a