Alpha plumbing has received a special one time order for 1500 faucets at $5 per unit. Alpha currently produces and sells 7500 units at 6 each. This level represents 75% of it's capacity. Production costs for these units are 4.50 per unit, which includes $3 variable cost and $1.50 fixed cost. In order to produce the special order, a new machine needs to be purchased at a cost of $1000 with a zero salvage value. Management expects no other changes in costs as a result of the additional production.

If Alpha wishes to increase it's profit by $1250 through the special order, the size of the order would need to be WHAT

Please explain in detail what the question is asking and how do we breakdown to solve the question

The answer apparently is 1125 units. But I am unsure how to arrive here.