A mass of $50g$ of crushed ice at an initial temperature

$0C$ is added to a thermos flask containing water at a

temperature of $20C.$

a$.$ Calculate the energy required to melt the ice.

b$.$ Determine the minimum mass of water that must

be present in the flask to melt the ice completely.

c$.$ Describe the final state of the system if the flask

initially contains less water than the value you

have calculated in $b.$