Stratosphere, Inc Inventory of Finished Goods on Hand at the Beginning of Quarter

Stratosphere, Inc. has the following budgeted sales for the next quarter.
$$\begin{array} { | l | r | r | r | } \hline \text { Month: } & \mathbf { 1 } & \mathbf { 2 } & \mathbf { 3 } \\\hline \text { Units } & 10,000 & 11,000 & 12,000 \\\hline\end{array}$$ Inventory of finished goods on hand at the beginning of the quarter is 4,000 units. The company desires to maintain ending inventory equal to beginning inventory plus 1,000 units every month.
Calculate the quantity to be produced during the quarter.