why is this lesson so tough

Dear Student,

Nothing is tough in mathematics. The thing which matters is your practice for a particular chapter. 

Mathematics is a kind of subject which demands a lot of practice and hard work. For practice you can refer to the chapter test, formative assessment, model tests etc. Also, for improving your content knowledge you can refer to the videos and examples provided in the chapter.

If you face any problem anywhere then do get back to us.