I think I am at extended abstract because I can create something that shows others how to do this.
First, you find the fractions:
1 3/8 and 5 1/8
Then you add them together because it asks how much milk did they drink in all.
Add the whole numbers first.
Then, you add the fractions, you add them by adding the numerators and keeping the denominator the same.
3/8 + 1/8= 4/8
Then you simplify 4/8 to 1/2
And you get 6 1/2