A column $50$ cm in diameter has a void fraction of $0\mathrm{.}36$ and it is run with a flow rate of $2$ liters$/$minutes$.$ In lab experiments it was determined that two solutes $($A and B$)$ show linear equilibrium adsorption on this gel $($K$1=6\mathrm{.}5$ and K$2=7\mathrm{.}0).$ What column length would be required to separate the two solutes by $7$ minutes