The dose d (in milligrams) of a particular medicine that a pediatrician prescribes for a patient varies directly with the patient’s mass m (in kilograms). The pediatrician recommends a dose of 150 mg of medicine for a patient whose mass is 30 kg.

a. Write a direct variation equation that relates m and d.
b. What would the dose of medicine be for a patient whose mass is 50 kg?