"10M bonds" denotes $10,000 in principal amount to be received by the bondholder at maturity. "6s" is short for bonds paying a 6 percent coupon rate. Each bond pays 6 percent annual interest of $60; thus, 10 bonds pay a total of $600 per year in two semiannual payments of $300. At maturity, bondholder will receive the $10,000 face amount plus the final semiannual payment ($10,000 + $300 = $10,300).