We have 10,000 severely delinquent accounts with an average balance of $4,000. Our internal collections team expects to recover 30% at a cost of $50 per account. An outside agency says it can recover 40%, but it keeps 25% of whatever it collects as commission. How would you compare the two in Excel, and what's the minimum recovery rate the agency needs to hit to be worth it?

我们有1万个严重逾期账户，平均欠款4000美元。内部催收预计回收30%，每户成本50美元；外包公司说能回收40%，但抽回收金额的25%做佣金。你在Excel里会怎么比较？外包的回收率至少要多少才划算？