Answer:
10.1 °C
Explanation:
After the mixture, heat is gained by the soapstone cubes (they were at a lower temperature) while heat is lost by the whisky (it was at a higher temperature).
Let the temperature of the mixture be <em>T</em>.
Heat lost by whisky, 
is the mass of the whisky (in kg),
is the specific heat of whisky (J/kg·K) and
is the change in temperature of the whisky (in °C or K).

Heat gained by soapstone cubes, 
There are three cubes of soapstone, so their mass is multiplied by 3.

From the principle of mixtures,
Heat lost by whisky = Heat gained by soapstone cubes (assuming no heat loss to the surroundings)




The final temperature of the whisky is 10.1 °C.