Answer:
 89 milliliters liquid was in the container before George added more .
Step-by-step explanation:
Let us assume that the liquid was in the container before George added more be x .
As given
George's container was partially full. 
Then he added 177 milliliters more liquid to the container. 
 Now the container has a total of 266 milliliters of liquid. 
Than the equation becomes 
liquid was in the container before George added more +  liquid added = Total liquid in the container 
Putting all the values in the above 
x + 177 = 266
x = 266 - 177
x = 89 milliliters 
Therefore 89 milliliters liquid was in the container before George added more .