a) The peak of the curve has coordinates (3, 45). Thus the maximum is 45 hundred dollars. It occurs when 3 hundred dollars are spent on advertisiing.
The maximum possible monthly profit of the shop is about $4500.
b) The x interval over which P(x) is greater than zero appears to be 0 to 10 hundred dollars. What is not clear from the question is whether the expected answer is (0, 10) or (0, 1000).
c) The maximum profit is earned when $300 is spent on advertising.
