我鐘意你同我講 I Love U, I Love U Too!
You are the sunshine of my life. That's why I'll always stay around. You are the apple of my eye. Forever you'll stay in my heart.
u treat 2/5 & 1 5/8 as 2 parts, let they are a and b.
and now all we need to find out is how much water is left if the total(sum) of these 2 parts which is poured into the 2litre bottle
so (2/5 + 1 5/8) - 2 or you can see (a+b)-2, its much easier