Mrs brewer and mrs flaws each ate 3/4 of there sandwich ms brewer ate more than mrs glawe.
how is that possible?

Imagine if Mrs Brewer ate a large sandwich and Mrs Flaws ate a small sandwich.  Then it is entirely possible for Brewer to eat more than Flaws because of the initial size of their sandwiches.

Or in other words 3/4 of a large sandwich is larger than 3/4 of a small sandwich.