$-10$ آب $\to 10{}^\circ C$ آب $\to 0$ یخ $m\to 0$ گرم یخ $40{}^\circ C$ آب $3400\to 10{}^\circ C$ گرم آب $20{}^\circ C$ آب $m\to 10{}^\circ C$ گرم آب آب: $Water$ / یخ: $Ice$ ${{Q}_{1}}+{{Q}_{2}}+...=0\Rightarrow (m{{c}_{\text{Ice}}}\Delta {{\theta }_{1}}+m{{L}_{F}}+m{{c}_{\text{Water}}}\Delta {{\theta }_{2}})+({{m}_{\text{Water}}}{{c}_{\text{Water}}}\Delta {{\theta }_{3}})+(m{{c}_{\text{Water}}}\Delta {{\theta }_{4}})=0$ $\Rightarrow m\times 2/1\times 10+336m+m\times 4/2\times 10+3400\times 4/2\times (-30)+m\times 4/2\times (-10)=0$ $\xrightarrow[4/2=2\times 2/1]{336=80\times 4/2}5m+80m+10m-(30\times 3400)-10m=0\Rightarrow 85m=30\times 3400\Rightarrow m=1200g$