Blake's gross income is $60,000, while that of his partner is $66,000.They plan to make a down payment of $50,000 on a $375,000 house.Their mortgage will be amortized over 25 years at a rate of 5% per annum, compounded semi-annually.Mortgage payments will be made monthly.They estimate monthly heating, property tax and consumer debt costs to be $200, $300 and $500, respectively.What will be their Gross Debt Service ratio?

a)29.6%

b)27.5%

c)25.4%

d)22.8%

The answer is 22.8%, could you please show the solution step-by-step? also, please show the solution using financial calculator if it's possible, thanks!