Studies show that after t hours on the job, the number of items a supermarket cashier can scan per minute is given by F.(t) = 80- 130 Answer parts (a), (b) and (c) below. 6+12 (a) Find F'(t), the rate at which the cashier's speed is increasing. F'(t)= (Simplify your answer. Use integers or fractions for any numbers in the expression.) 13