How do I answer this question?

Question

On Monday, Mr. Smith bought a gallon of milk for his family. On Wednesday, there was only 1/4 of a gallon left. His son drank 2/3 of that milk for breakfast. How much of the gallon of milk was left?

I was thinking that is:

1/4x2/3=2/12 left

but this was marked incorrect what am I doing wrong?

Answer 1

3/4 of the gallon was consumed.

The son drink 2/3 * 3/4 = 6/12 = 1/2 gallon