Pine Street Inc. makes unfinished bookcases that it sells for $58 . Production costs are $37 variable and $11 fixed. Because it has unused capacity, Pine Street is considering finishing the bookcases and selling them for $75 . Variable finishing costs are expected to be an additional $6 per unit with no increase in fixed costs. Prepare an analysis on a per unit basis showing whether Pine Street should sell unfinished or finished bookcases. (Enter negative amounts using either a negative sign preceding the number e.g. -45 or parentheses e.g. (45).)