Trying to figure out, without the use of an excel function how to solve for an interest rate of a mortgage knowing the following paramaters.

initial principal balance - 200,000

total interest paid - 279,017.80

years amortized - 30

payments/yr - 12

If it helps any the answer is 7%.

I use the RATE function in excel and it works fine, but again trying to solve without that function.. Thank you!

John