A. f(155) = 425 means that if a patient weighs 155 pounds, the recommended dosage of vitamin B-12 is 425 micrograms.
B. f'(155) = 20 means that the rate of change of the dosage with respect to weight at a weight of 155 pounds is 20 micrograms per pound. In other words, for every one-pound increase in weight at 155 pounds, the dosage is expected to increase by 20 micrograms.
C. To estimate the dosage for a person weighing 175 pounds, we need to know the specific function or equation that defines the relationship between dosage and weight. Without this information, we cannot estimate the dosage accurately.