CFA mock PM Q13

Could somebody please explain how we are suppost to know that the mortgage is 4 months old. Personally I felt this Q is really unfair. Hope there will not be like this on exam

agree- I messed that one up too.

It is given that the mortgage is 30 yr mortgage. That means 360 payments (30x12). In the second paragraph it says, WAM(weighted average maturity) of 356 which means 4 months old