How did she get 12.28 % ? show the work please with simple steps

Incremental Borrowing Cost Alternative #1 Alternative #2 LTV 90% 80% i 8.5% 8% 30 Years 30 Years $15,000 $30,000 $135,000 $120,000 $1,038.03 $880.52 Notes Term Down payment Loan Payment M stv AL R Comments A 20 Borrow $15,000 more. Pay $157.51 per month more. cremental Borrowing Cost. Cash Flow Differences. PV = $15,000 PMT = $157.51 n = 360 FV = $0 CPT N=360 J/Y = ? PV = 115,000 = 12.28% PM7=-157.31 FV = 0