First of all, we can know from the first equation that three cups are thirty, so one cup is ten yuan;
The second equation shows that a drink plus two hamburgers equals twenty, and a drink is ten yuan, that is to say, two hamburgers are ten yuan, so a hamburger is five yuan;
The third equation shows that a hamburger with four packages of French fries is pet-name ruby, and a hamburger is five yuan. If you get four bags of French fries, one bag of French fries is one yuan.
The last question is a bag of French fries (1) multiplied by a drink (10) and a hamburger (5).
So the process of this problem is 1* 10+5= 15.