Question: Thermal-Equilibrium

Two glasses of water with the same amount of water, one glass (a) was at 20.8 °C and the other was 46.3 °C – glass (b).
mixing water

When they were mixed what was the final temperature?

20 °C – 30 °C: temperature of glass (a)

30 °C – 40 °C: half way between (a) and (b)

40°C – 50°C: temperature of glass (b)