The problem with this question is that we don't know if the interest rate of 6% is nominal or effective.

A nominal interest rate is different from the effective if the period of time after that the interest is credited (e.g. a month) is not identical to the basic time unit (normally a year).

For example, let's assume a nominal interest rate of 6% which is credited as of 6%/12 = 0.5% every month. After one year, the initial capital is increased by the factor (1+0.005)^12 = 1.0616. As a result, this nominal interest rate is equivalent to an effective interest rate of 6.16%.

Therefore, the correct calculation will consider an interest rate of 6.16% and the final result will be a monthly payment of $832.43.

On the contrary, if the 6% corresponds to an effective interest rate, the final result will be in fact $828.64.

BTW $736.11 is the value you get for simple interest, which is not the case for this is compound.

Source(s):
http://en.wikipedia.org/wiki/Interest

http://en.wikipedia.org/wiki/Nominal_interest_rate

http://www.bankrate.com/brm/popcalc2.asp?unroundedPayment=828.644394673625&loanAmount=50000.00&nrOfYears=6.00&nrOfMonths=72&interestRate=6.16&startMonth=5&startDay=21&startYear=2006&monthlyPayment=+++++%3D%3D%3D%3E&showAmort=Show%2FRecalculate+Amortization+Table&monthlyAdditional=0&yearlyAdditional=0&yearlyAdditionalMonth=5&oneAdditional=0&oneAdditionalMonth=5&oneAdditionalYear=2006&paidOffDate=Jun+21%2C+2012