$3\mathrm{.}89$ As shown in Fig. P$3\mathrm{.}89,$ a tank open to the atmosphere initially contains $2lb$ of liquid water at $80F$ and $0\mathrm{.}4lb$ of ice at $32F.$ All of the ice melts as the tank contents attain equilibrium. If no significant heat transfer occurs between the tank contents and their surroundings, determine the final equilibrium temperature, in $F.$ For water, the specific enthalpy change for a phase change from solid to liquid at $32F$ and $1$atm is $144Bt\frac{u}{l}b.$

Fig. P$3\mathrm{.}89$