If the recommended adult dosage for a drug is D(in mg), then to determine the appropriate dosage

Question:

If the recommended adult dosage for a drug is D(in mg), then to determine the appropriate dosage c for a child of age a, pharmacists use the equation c = 0.0417 D(a + 1). Suppose the dosage for an adult is 200 mg.
(a) Find the slope of the graph of c. What does it represent?
(b) What is the dosage for a newborn?