Answer:
Not sure if this is right but it might be something like
350,000-4%+1671m
or
3500,000-4%y/1671m
Explanation:
The numbers we know are 350,000 4% and 1671 per month
350,000 is the full mortgage
4% is the APR or annual percentage rate like interest
and we know the monthly for the mortgage is 1671 per month