540 g of ice at 0^oC is mixed with 540 g of water at 80^oC. The final temperature of the mixture is

Heat taken by ice to melt at 0^oC,

${\mathrm{Q}}_1=\mathrm{mL}=540\times 80=43200\mathrm{cal}$

Heat given by water to cool upto 0^oC,

${\mathrm{Q}}_2=\mathrm{ms\Delta \theta }=540\times 1\times (80-0)=43200\mathrm{cal}$

Hence heat given by water is just sufficient to melt the whole ice and final temperature of mixture is 0^oC.