Cullumber Street Inc. makes unfinished bookcases that it sells for $58. Production costs are $38 variable and $10 fixed. Because it has unused capacity, Cullumber Street is considering finishing the bookcases and selling them for $74. Variable finishing costs are expected to be $7 per unit with no increase in fixed costs. Prepare an analysis on a per unit basis showing whether Cullumber 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).)