A company purchased $200$ units for $$20$ each on January $31.$ It purchased $200$ units for $$30$ each on February $28.$ It sold a total of $270$ units for $$110$ each from March $1$ through December $31.$ If the company uses the last $-$ in$,$ first $-$ out inventory costing method, calculate the cost of ending inventory on December $31.($Assume that the company uses a perpetual inventory system.$)$

A$.$ $$11,700$

B$.$ $$3,900$

C$.$ $$130$

D$.$ $$2,600$