I don't really know how to approach this problem. Help please.

On a 30-year, fixed rate mortgage with a 3.5% APR, how long does it take before the majority (ie, > 50%) of your payment starts going toward principal rather than interest? Try solving and using calculator functions vs solving in Excel 0 7 year, 8 month 15 year 17 year, 1 month 10 year, 3 month 0