$100$ $kg$ of a feed containing $50$ $wt.\%$ of a solute $C$ is contacted with $80$ $kg$ of a solvent containing $0.5$ $wt.\%$ of $C$ is a mixer-settler unit. From the operation, the resultant extract and raffinate phases contain $40$ $wt.\%$ and $20$ $wt.\%$ of $C$, respectively. If $E$ and $R$ denote the mass of the extract and raffinate phases, respectively, the ratio $E/R$ is
1. $1/4$
2. $1/2$
3. $2/3$
4. $1$