We have $$W = 10 + 0.895m -12.33c^{0.18} + 12.33c^{0.18}$$
we calculate the differential of m, which is $0.895$ and the differential of $c$, which is something like $$-12.33/c^{0.82} + 12.33/c^{0.82}$$ and what then?
what do we do with $c$. I am confused...