1/3 of a cup = 3/9 of a cup. If you have 7/9 of a cup, the most 3/9ths that can fit in it is two 3/9ths, which equals 6/9. 6/9 < 7/9. Another latte would give you 9/9, and 9/9 > 7/9 so that's not possible. So two lattes can be made with 7/9 cups of milk.
