What is the relation between Rate of reaction and rate of consumption of reactants?
For your first part you're supposed to multiply it by -3 instead if $\frac{-1}{3}$  as the rate of reaction is given for one mole. That is if $R$ is the rate of reaction it is defined as .
$$\frac{-d[A]}{dt} = \frac{-d[B]}{3dt} = \frac{d[C]}{2dt} = R$$
So the rate of consumption of B is $-3R$.



As for your second part it's a tad unclear for me if you could further edit your question.I could take a shot at answering your second part as well