It's asking what is the theme of the story, the message the author is trying to convey, in five complete sentences. You can word it like this:
El mensaje que el autor trata de expresar es ...
Which translates to:
The message the author is trying to convey is ...
Quiero is the right answer because Victor is talking in first person, so in english he would be replying with "I want to pay with a credit card." As opposed to saying "we want...or you want...or he wanted" because Fernando asked Victor "how are you going to pay?"
I think the sentence is grammatically correct when written as "Los peces no dormen."
"Los peces no dormen." means "Fish do not sleep." which in my opinion is grammatically correct.
40/360: .1~ litro de gasolina por un km
