What effect would you expect the following changes to have on the rate of the $\mathrm{S}_{\mathrm{N}} 2$ reaction of 1 -iodo-2-methylbutane with cyanide ion?
(a) The CN $^{-}$ concentration is halved, and the 1 -iodo-2-methylbutane concentration is doubled.
(b) Both the $\mathrm{CN}^{-}$ and the 1-iodo-2-methylbutane concentrations are tripled.