the answer should be negative

Average Cost Jester Sports manufactures tennis rackets. The total cost of producing r rackets per hour is given by C(x) = 0.49 x-+ 6 2 + 444. The average cost per racket at production level a rackets per hour is C (a) = C(x) Use differential approximations to estimate the change in average cost per racket if the production is increased from 20 per hour to 24 per hour. Round to the nearest cent. $ per racket NOTE: Your answer may be negative