A firm manufactures hard disk drives and sells them for $107 each. Each drive requires raw materials costing $24. The number of units sold and total wages bill (including full-time and casual staff) for each of the last 6 months are as follows. Which of the following is the best estimate of the variable component of this semi-fixed wages cost? on Aug Jul Sep Oct Nov Dec 40 Sales 38 37 26 29 39 Wages 1900 1840 1809 1479 1869 1571 Select one: a. $30 b. $25 x c. $20 d. $45