Heat energy liberated by #540 g# of water to cool down to #0^@C# is #540*1*(80-0) C=43200 C# (using, #H = ms d theta# ,where, #m# is the mass, #s# is the specific heat and #d theta # is change in temperature)
Now,heat energy required for #540 g# of ice to get converted to same amount of water at #0^@C# is #540*80=43200 C# (using, #H=ml# where, #l# is the latent heat of melting of ice = #80 C/g#)
So,the required heat energy for the given amount of ice to get converted to water at #0^@C# will be supplied exactly due to the cooling of water to #0^@C#, so total #540+540=1080g# of water will be present at #0^@C#