If for every $1000 you pay 608 how much would that be if you borrow $300,000?

I believe that you meant to say that for every $1000 the payment is $6.08, not $608. At $6.08 per $1000, assuming a 30 year loan, that would translete to an interest rate of 6.131%. Take $6.08 x 300 = $1824/mo for a $300,000 loan.

If you pay x amount per 1000 and you want to find the amount you would pay for $300K, then its simple multiplication.

Windows comes with a calculator under Start>Accessories. I suggest you learn to use it.