What mass of cold water at a temperature of 15 degrees must be poured into hot water with a volume

What mass of cold water at a temperature of 15 degrees must be poured into hot water with a volume of 4 liters at a temperature of 95 degrees in order to get water equal to 35 degrees.

Q1 = Q2.
Q1 (heating cold water); Q1 = C * m1 * (t3 – t1); C is the specific heat capacity, m1 is the desired mass, t3 is the equilibrium temperature (t3 = 35 ° C), t1 is the beginning. temperature (t1 = 15 ° С).
Q2 (hot water cooling); Q2 = С * m2 * (t2 – t3); m is the mass of water (a volume of water of 4 liters corresponds to a mass of 4 kg), t2 is the beginning. temperature (t2 = 95 ° C).
С * m1 * (t3 – t1) = С * m2 * (t2 – t3).
m1 * (t3 – t1) = m2 * (t2 – t3).
m1 = m2 * (t2 – t3) / (t3 – t1) = 4 * (95 – 35) / (35 – 15) = 4 * 60/20 = 12 kg.