Temperature of solution A = 12°C
Let the temperature of solution B , be x as we dont know it's actual temperature .
Temperature of new solution = 0°C
The above statements can be written in an equation as :-
[tex]12 + x = 0[/tex]
[tex]x = 0 - 12[/tex]
[tex]\color{olive}\implies\color{hotpink}x = ( - 12)[/tex]
Let us check whether or not we have found out the correct temperature of Solution B by placing -12 in the place of x :-
[tex]12 + ( - 12) = 0[/tex]
[tex]0 = 0[/tex]
[tex]\color{hotpink}LHS = RHS [/tex]
As the left hand side of the equation is equivalent to the right hand side of the equation, we can conclude that we have found out the correct temperature of solution B .
Therefore , the temperature of Solution B = (-12)°C .