On January $1$ of the current year, Barton Corporation issued $8\%,5-$year bonds with a face value of $$105,000.$ The bonds are sold for $$99,750.$ The bonds pay interest semiannually on June $30$ and December $31,$ and the maturity date is December $31,5$ years from now. Barton records straight$-$line amortization of the bond discount. The bond interest expense for the current year ended December $31$ is

a$.$ $$9,450$

b$.$ $$525$

c$.$ $$9,975$

d$.$ $$4,200$