For a company that manufactures tennis​ rackets, the average cost per racket is found to be C= 360 x+4+ 1 3x for x≥1​, where x is the number of rackets produced per hour. Use the differential to approximate the change in average cost per racket if production is​ (A) increased from 20 per hour to 27 per hour and​ (B) increased from 45 per hour to 52 per hour.