I'm sorry, do you have any more detail. i'm not sure what this means?
Can you repost with the picture please
So, Using your conversion chart(if you have one) you'd see 1 liter makes 1000 milliliters. So, if you have half of a liter(0.5), then you have 500 milliliters. If he adds 300 more, then you get 800 milliliters total, which is also equal to 0.8 liters. Hope this helps!
"The branch of mathematics concerned with the properties and relations of points, lines, surfaces, solids, and higher dimensional analogs." - Dictonary.com
In simple words, it is a study in math in which you study shapes, lines, planes, and points.