You would have to divide 18.9 by 5, as you're cutting 18.9 into 5 equal parts. Using long division, you can solve this. I have attached an image below for reference:
One liter is 1,000 ml. plus 299 ml. is 1,299 ml. plus the additonal 398 ml. is 1,697 ml. which is 722 ml. less than the total volume. (722 ml. of water can still be added.)
