Three liquids are at temperatures of 10 ◦C, 19◦C, and 33◦C, respectively. Equal masses of the first two liquids are mixed, and the equilibrium temperature is 15◦C. Equal masses of the second and third are then mixed, and the equilibrium temperature is 28.9 ◦C. Find the equilibrium temperature when equal masses of the first and third are mixed. Answer in units of ◦C.