"Because the class is difficult, I study at home."
Adjective noun would be translated as: "Because of the interesting class" which is different meaning
You probably meant "Because of the DIFFICULT class", right? Still very helpful comment.
No, に is usually used for a destination for a verb, not the location you do it at. So, say, to use a different verb, あるきます (to walk), いえにあるきます means "I walk (to) home" whereas いえであるきます would be "I walk at home" (ie, I'm walking around inside my house).
I had it the first part if the sentence ordered adjective -> noun. It says its the other way around. I feel confused now.
Duolingo should provide a report option for reporting missing words in the word bank input feature... The word むずかしい or any partial pieces of it was not listed in the word bank, so I could not use this and had to input the characters with another method. There have been problems before with some words being strangely divided between word bank pieces, too, so please add the option "word bank is unnatural or has an error" to the reporting feature.
For these kinds of situations, you can report the bug here:
Why didn't the "kara" go between here!? This app is all set the place!