18. Given the following information, what is the IRR of the residual class? A CMO is being issued with 3 tranches. The issue will be overcollateralized by S3M and the issuer (residual) will receive cash flows only after all classes of investors have been completely repaid. Priority payments will be made to the A tranche and will include the promised coupon. Interest will be accrued to the Z tranche until A is completely repaid. The B class will receive interest payments only until the A class is repaid. The A class will then receive all remaining CFs from the pool that year. After A is repaid, B will receive priority principal payments. The Z class will accrue interest at 8% until both A and B are repaid. It will receive current interest and principal payments at that time. At the beginning of year 10 (the final year in the security) there is S5M outstanding in principal owed to class Z investors. Additionally, the pool of mortgages generates $20,528,131 in cash flows in year 10 A. 11.71% B. 12.00% C. 17.56% D. 17.87% E. 21.21%