I have some doubts about the following issue. Let's say that we have a sentence:
It's difficult to perform the calculations.
Now, I want to make "the calculations" the subject of this sentence, so I write:
(1) The calculations are difficult to be preformed.
But is it correct not to use the passive voice? Something like that:
(2) The calculations are difficult to preform.
I thought that the passive is mandatory in such cases, but then I saw the following example from Cambridge Dictionary:
This meat is difficult to chew.
So, it isn't fully clear to me how to use it correctly. I would write something more like
This meat is difficult to be chewed.
Could anyone comment on that issue?