Brian borrows $15,000 from Mary and agrees to repay with 12 installments payable half-yearly. The effective interest rate is 6.09% per annum. When the 6th payment is due, Brian repays the outstanding loan balance by a lump sum.

a.) Calculate the lump sum payment of Brian

b.) Calculate the loss of interest income of Mary

Please show all work by hand, without using a finance calculator or Excel. Thank you.