Final answer:
The optimal order quantity using the fixed-order quantity model is approximately 2218 units.
Step-by-step explanation:
The optimal order quantity using the fixed-order quantity model can be calculated using the Economic Order Quantity (EOQ) formula.
EOQ = sqrt((2 * annual demand * ordering cost) / holding cost)
Substituting the given values:
EOQ = sqrt((2 * 25913 * 19) / 4) = sqrt(4928978.5) = 2218.28
Therefore, the optimal order quantity is approximately 2218 units.