ABC Furniture is trying to figure out how to minimize its cost when producing couches each month. To figure out where their unit costs are the lowest, they give you the following information:

Each couch takes $250 of materials. Each couch takes $200-worth of wages for workers to produce. The factory owner knows that during regular hours they can produce 20 couches each month. After 20 couches, they need to keep the laborers into overtime. In overtime, they must pay the workers time and a half (1.5x their regular wage). The owner also knows that after 25 couches, the workers need to stay into double overtime (2x regular wage). The factory's rent is $2,500 a month.

If the firm wants to minimize its average total cost per couch, how many couches should they produce?