The interest rate is "simple", so he will pay 7% extra of what he borrowed back per year.
7% of $18,500 is $1,295
So over 3.5 years, he'll need to pay $1,295 x 3.5 which is $4,532.50 interest.
But remember he also owes the original amount he borrowed, so he'll owe $18,500 + $4,532.50 which is $23,032.50 total
Hope this helped
