Pour B glass of water into A cup until A cup is full.

Then 1/2a glass of water is poured from the B cup to the A cup.

At this time, there is (b- 1/2a) water left in the B cup.

There should be 1/2a glass of milk and 1/2a glass of water in a cup.

Then pour this mixed liquid into cup B and fill it up.

Is to pour 1/2a cups of mixed liquid.

That is, 1/4a cup of milk and 1/4a cup of water.

There is 1/4a glass of milk in glass B.

There are 1/4a cups of milk left in a cup.