Finding equilibrium temperature when two things are mixed 10 g of ice at −10 °C is added to 10 g of water at 85 °C. What is the final temperature and amount of ice left in the system? (System is kept inside an ideal insulator)

This question may seem quite easy for many of the readers, but please help me with such questions as I find them tricky. I understand that this is a question which involves the application of the $Q=mc\,\delta T$ formula and that we have to equate the $Q$'s of both ice and water in order to obtain the answer.
Another thing which is troubling me is that the answers to most of such questions that I have encountered is 0 °C, and this question is not an exception.
Please suggest me on how to go about such questions, and provide some conceptual clarity on the topic if possible.
In this type of question, you should bring all the matter into one state and calculate net heat.
In this solution, we will consider heat released as positive heat, absorbed as negative, and the state to which we will bring all the matter be water at 0 °C.

Here we were left with 20 g of water at 0 °C and zero heat if heat was some positive quantity we would use the heat to raise 20 g water to a specific temperature.
By equation $20\times T\times1=\text{heat left}$
$T$ is temperature to which 20 g water is raised
If heat was negative quantity, we would convert part of water at 0 °C to ice at 0 °C by equation
$M\times80=\text{heat left}$
$M$ mass of water which is converted to ice