A mixer holds a solution whose concentration is C(t)=V(t)m(t). At a particular moment, m=500 g and V=250 L. The salt is being added at dtdm=2 g min−1 while the solution drains at dtdV=−4 L min−1. Determine dtdC at that moment (in g L−1 min−1).
a) 0.032
b) 0.04
c) −0.04
d) −0.024