They go back to this formula. If you sold it after five years, then there are twenty-five years left, so 25 x 12 is the number of months left; they plug that into this formula.

如果五年后卖掉房子,他们又搬出公式,此时剩余期限是20五年,所以剩余月份数是25乘以12,把月份数代入这个公式

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