Formulate a linear programming model for this problem.

(I'm especially confused about whether to use an unequal sign or an equal sign: about the factory's output. What should it be or = ?)

3.17.* The Medequip Company produces precision medical diagnostic equipment at two factories. Three medical centers have placed orders for this month's production output. The following table shows what the cost would be for shipping each unit from each factory to each of these customers. Also shown are the number of units that will be produced at each factory and the number of units ordered by each customer. A decision now needs to be made about the shipping plan for how many units to ship from each factory to each customer. \begin{tabular}{lrrrr} \hline & \multicolumn{3}{c}{ Unit Shipping Cost } & \\ \cline { 2 - 4 } From & & & \\ \hline Factory 1 & Customer 1 & Customer 2 & Customer 3 & Output \\ \hline Factory 2 & 4600 & $800 & $700 & 400 units \\ \hline Order size & 300 units & 900 & 600 & 500 units \\ \hline \end{tabular}