I wonder whether following sentence is grammatically correct?
"It could have been that I wouldn't have been able to solve even one of these two problems, let alone both of them."
I'm talking here about a past exam that I took. It had 2 problems and I was able to solve both of them. What I'm trying to say is that it was by no means guaranteed that I would have been able to solve either of the 2 problems, and even less so that I'd solve not just one but both of them.
In general, I want to talk about a hypothetical in the past without the "if" conditional and by starting the sentence with "it could have been that...".