Question: Let P(x) be the number of people of height ≤ x inches in the US. What is the meaning of P'(66)? What are its units? Estimate P'(66) (using common sense). Is P'(x) ever negative? [Hint: You may want to approximate P'(66) by a difference quotient, using h = 1. Also, you may assume the US population is about 300 million, and note that 66 inches = 5 feet 6 inches.]