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-느라(고) is a cause-and-effect particle that is commonly used for making excuses.
A few examples of the usage taken off from talktomeinkorean.com are:
1) 일하느라고 못 갔어요. I had to work, so I couldn't go.
2) 시험 준비 하느라고 바빵요. I had to study for an exam, so I was busy.
3) 학비를 내느라고 돈을 다 썼어요. I had to pay my tuition fees, so I used all my money.
Take a look at this http://www.talktomeinkorean.com/lessons/l7l9/ if you want a more detailed explanation. I hope I helped!
