CMBS Issue, $$500$M of senior security and $$100$M Mezzanine security. Coupon rate for senior is $7\%$ and $9\%$ for mezzanine. The average Contractual interest rate in the underlying mortgage pool is $10\%.$ With an annual interest payment and no$-$par value is retired or defaulted on$,$ how much interest is available for IO tranche at the end of the end the first year?