For a company that manufactures tennis rackets, the average cost per racket is found to be C=- 360 1 +7+x for x 21, where x is the number of rackets X produced per hour. Use the differential to approximate the change in average cost per racket if production is (A) increased from 15 per hour to 19 per hour and (B) increased from 35 per hour to 39 per hour. (A) If production is increased from 15 per hour to 19 per hour the average cost per racket will by approximately $ per racket. per racket. (B) If production is increased from 35 per hour to 39 per hour the average cost per racket will by approximately $