Relative clause more formal

[Zimtstern]

Good evening everyone,

I have a question regarding relative clauses: I am supposed to rewrite the clauses to make them more formal.
Now, I am aware that in a formal clause you put the preposition before the relative pronoun. But here is one sentence that is not quite clear to me:

"I went to the lecture, and just about understood most of it."
My suggestions for a more formal way would be: I went to the lecture, of which I just about understood most.
But it doesn't sound quite right to me. Can anyone help me out?

Thanks!

[Alan]

--> I went to the lecture, most of which I just about understood.