Simple,
first find out how many fluid ounces there are in 1 cup
1 cup=8 fluid ounces
That means for Anu:
2*8=16
Anu has drunk 16 fluid ounces.
Now, Jan, we know that she drinks 2x (twice) as much as Anu...
So,
4 cups:
4*8=32
Thus, it means that Jan has drunk 32 fluid ounces.