Why the answer is 2100? It was supposed to be 400. Could you please tell me the right answer?

12/4 Purchased office supplies on account for $1,000. Payment is due in 30 days Office Supplies on hand on December 30th are $600. \begin{tabular}{|l|l|r|r|} \hline 4 & Supplies Expennse & 2,100 & \\ \hline & Supplies & & 2,100 \\ \hline \end{tabular}