CMO Question

Hey guys, I am having trouble with this problem. I can do it on excel, but how would you do this qucikly w a calc? Suppose you are the fixed income portfolio manager for a small insurance company and you are considering the purchase of CMO structure. This structure consists only of a Planned Amortization Class tranche and a Support tranche. a. Suppose that the during the first 36 months of the existence of the CMO, prepayment speeds averaged 75 PSA while the initial PAC collar was 90 to 200 PSA. What are the implications of this information, when you are considering the PAC bond for possible investment?

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