karlson roller skates has three product lines—​d, ​e, and f. the following information is​ available: d e f sales revenue ​$90,000 ​$40,000 ​$30,000 variable costs ​(30,000) ​(10,000) ​(12,000) contribution margin ​$60,000 ​$30,000 ​$18,000 fixed costs ​(10,000) ​(15,000) ​(23,000) operating income​ (loss) ​$50,000 ​$15,000 ​$(5,000) the company is deciding whether to drop product line f because it has an operating loss. assuming fixed costs are​ unavoidable, if karlson drops product line f and rents the space formerly used to produce product f for​ $18,000 per​ year, total operating income will be​ .