Hey guys, so I'm doing a few questions on related rates and differential approximation and I am stuck on this one, if anyone could offer ANY help at all I would be extremely grateful! Certain chemotherapy dosages depend on a patient's surface area. According to the Mosteller model
 S = √(h M) 6
where h is the patient's height in m, M is the patient's mass in kg and S is the patient's approximate surface area in m2. Assume that the patient's height is a constant 174 cm but he is on a diet. If a patient loses 3.5 kg per month, how fast is his surface area changing (in m2/month) at the instant his mass is 60 kg? Give your answer correct to 4 decimal places.
Note. You may be wondering why we have referred to the patient's mass here, rather than his weight. Technically, a person's weight is a force (recall: F = Ma, where F is the force, M is the mass, and a is the acceleration, which in this case is g, the acceleration due to gravity). Force (and therefore weight) is measured in Newtons, not kilograms. Scientists, and you are one, should know that. (In orbit, an astronaut experiences weightlessness, not masslessness.)

$S(M)=\frac{\sqrt{hM}}{6}$
$\left.\frac{dS}{dt}\right|_{M=60}$