How to determine the composition of a mixture between liquid water and ice from temperature and heat graph?

Jun 2017
Lima, Peru
The problem is as follows:

The graph from below shows Temperature with respect of heat in the thermal interaction between a sample of $400\,g$ of liquid water and another sample of $200\,g$ of ice. What is the final composition of the mixture?

The alternatives given are as follows:

1.&\textrm{400 g. of liquid water and 200 g. of ice}\\
2.&\textrm{400 g. of liquid water and 25 g. of ice}\\
3.&\textrm{600 g. of ice}\\
4.&\textrm{600 g. of liquid water}\\
5.&\textrm{575 g. of liquid water and 25 g. of ice}\\

I'm not sure exactly how can I get the composition of the mixture. I'm assuming that the horizontal line from which is not given any information of the heat represents the transition between the solid and liquid phase. But how can the composition of the mixture be found?. Can somebody help me here please?.