am i missing something? problem, question, something, comparable

hanvinh

on Pg 88 , CFA Text Book -Volume 4, in the answer to problem 23, it says MCC is estimated
by YTM on comparable outstanding.But the outstanding debt has a 9% YTM as compared to 7% in the new issue.

My question : Why is 7% YTM used for outstanding debt calculation?

Thanks!