There is a metal cup ($($mass =$=$ m1)$1)$ with a temperature ($($T1)$1)$ and a mass of water ($($m2)$2)$ with a higher temperature ($($T2).$2).$ The cup has a heat capacity of c1=($1=($c0)($0)($T/'" id="MathJax-Element-12-Frame" role="presentation" style="font-size: 121%; position: relative;" tabindex="0">/'$/\text{'}$tau')," id="MathJax-Element-13-Frame" role="presentation" style="font-size: 121%; position: relative;" tabindex="0">'),$\text{'}),$and the water has a heat capacity of c2.$2.$ c0$0$ and 'tau' are known constants. Write an equation to solve for the equilibrium temperature ($($Tf)$)$ when the water is poured into the cup.