Two liquids A and B are in the ratio $5: 1$ in container $1$ and in container $2$, they are in the ratio $1: 3$. In what ratio should the contents of the two containers be mixed so as to obtain a mixture of A and B in the ratio $1 : 1$?

- $2:3$
- $4:3$
- $3:2$
- $3:4$