Translation:Plane tickets become more and more expensive.
I'm sure that きっぷ is used for the physical piece of paper, so is used more for bus ticket, metro ticket etc. because you physically have a ticket from the ticket machine. A airline ticket is issued electronically and so technically what you print out is the receipt and thus チケット is used. One of those tricky things in Japanese...
Showing your age here, but plane tickets used to be pièces of paper. Also I buy physical bus/train tickets a couple of times a year at most. This is not the distinction you're looking for…
It's just more fashionable to use English loan words these days. That's all there is to it.
This is an awkward translation in English. "more and more expensive" would be paired with "are getting" or "have become". I think the Japanese Duo is too literal in these translations. It is better to insist on natural speech in either language and let learners figure out the differences.
This sentence is incredibly asinine in its required translation. If i use "become", it says Im wrong unless I put "will" in front of it. If I use "get" with "will", it says Im wrong and I need to use "become" but shows an example sentence that isnt using "will"?? Its said Ive gotten it wrong four times in a row because of all this and im so frustrated.
I believe that is what the だんだん does; without it, this would mean something like "The plane tickets will become more expensive," (future tense because that's the only way I can think to say it) whereas with it, translates to "the plane tickets become more and more expensive."
I hope that helps.