Shelley Company produces a machine that requires four pistons. They feel that they must produce 200,000 machines next year. They want to hold, in their ending materials inventory, enough pistons to meet 10% of next year's production requirement. They will start the year with enough pistons to manufacture 10,000 machines. How many pistons must they purchase? \begin{tabular}{|} \hline 840,000 \\ \hline 630.000 \\ \hline 660.000 \\ \hline 645,000 \\ \hline 615,000 \\ \hline \end{tabular}