Final answer:
The cost of each shirt would be approximately €8.63.
Step-by-step explanation:
To find the cost of each shirt when purchasing 40 shirts, we can use the function given: P'(s) = -0.004s, where s is the number of shirts purchased. We are given that 9 shirts cost €9.75 each, so we can substitute s = 9 and P = 9.75 into the function to find the rate of change in the unit price: P'(9) = -0.004(9) = -0.036.
To find the cost of each shirt when purchasing 40 shirts, we can multiply the rate of change by the number of additional shirts from 9 to 40: -0.036(40-9) = -0.036(31) = -1.116.
To find the new unit price, subtract the rate of change from the original cost of each shirt: 9.75 - 1.116 = 8.634. Therefore, each shirt would cost approximately €8.63.