The weight, W, in lbs, of a child is a function of its age, a, in years, so W = f(a).
(a) Do you expect f'(a) to be positive or negative? Why?
(b) What does f(8) = 45 tell you? Give units for the numbers 8 and 45.

(c) What are the units of f'(a)? Explain what f'(a) tells you in terms of age and weight.

(d) What does f'(8) = 4 tell you about age and weight?

(e) As a increases, do you expect f'(a) to increase or decrease? Explain.