On January $1$ of the current year, Barton Corporation issued $9\%$ bonds with a face value of $$64,000.$ The bonds are sold for $$62,080.$ 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 year ended December $31$ is

a$.$ $$1,920$

b$.$ $$480$

c$.$ $$5,760$

d$.$ $$6,144$