Rate law for substitution reaction of 2-bromobutane with $\stackrel{\mathrm{\Theta }}{\mathrm{OH}}$ in 75% ethanol and 25% water at ${30}^0\mathrm{C}$ is rate $=3.20\times {10}^{-5}$ (2-bromobutane) $\left[{\mathrm{OH}}^{-}\right]+1.5\times {10}^{-6}$ (2-bromobutane) what percent of reaction take place by ${\mathrm{S}}_{\mathrm{N}}2$ when $\left[{\mathrm{OH}}^{-}\right]=1.00\mathrm{M}$? (Answer must be in nearest whole number)