Teresa makes sweaters in her home. Starting with just some knitting needles and yarn, she was able to knit 50 sweaters per year. Now some local stores have expressed interest in her designs and offered to buy her sweaters for $20 each. This makes it worthwhile for her to invest in some capital; in particular, she could produce many more sweaters if she invested in one or more looms, as shown in the following table. Assume that Teresa's sweater business is a perfectly competitive firm.