Fixed vs variable cost preference. bates operates a kiosk at a local mall, selling duck calls for $30 each. the variable cost to make a duck call is $18. a new mall is opening where bates wants to locate a new kiosk. the mall operator offers the following two options for bates: 1. paying a fixed rent of $15,000 a month, or: 2. paying a fixed rent of $9,000 per month plus 10% of revenue earned from each duck call, the amount of monthly sales (in units) at which bates would be indifferent as to which plan to select is: a) 1,900 b) 2,000 c) 1,500 d) 1,600