Riggs Company purchases sails and produces sailboats. It currently produces 1,280 sailboats per year, operating at normal capacity. which is about 80% of full capacity. Riggs purchases sails at $258 each, but the company is considering using the excess capacity to manufacture the sails instead. The manufacturing cost per sail would be $91 for direct materials, $87 for direct labor, and $90 for overhead. The $90 overhead is based on $78,080 of annual fixed overhead that is allocated using normal capacity. The president of Riggs has come to you for advice. "It would cost me $268 to make the sails," she says, "but only $258 to buy them. Should I continue buying them, or have I missed something?" (a) Prepare a per unit analysis of the differential costs. (Enter negative amounts using either a negotive sign preceding the number eg. -45 or parentheses eg. (45)) Should Riggs make or buy the sails