Answer-
Graham paid an interest of $111,000.
Solution-
The mortgage amount is $150,000
The amount of money Graham is paying monthly = $725
Time = 30 years = 30 × 12 = 360 months
So, the total amount of money paid by him is,

As interest is the extra amount of of money paid upon the original value, so

Therefore, Graham paid an interest of $111,000.