Struggle with or Struggle against

You struggle with something when it's something difficult to handle, when it takes a lot of effort, etc. It means that you try hard to do something very difficult.

You struggle against something/someone when you want to overcome someone or some force. Or you struggle against someone/something to defeat them or to cease them to have power over you.

Thanks! Let me see if I got it now, are these sentences correct?
I'm struggling with this math exercise
I'm struggling against deforestation

I'm struggling with this math exercise
I'm struggling against deforestation

As duas frases acima estão corretas.

Yes, Goulart. You got them right.
As a grammar aside, at the end of a sentence you can use period (punctuation). Periods, like family and relatives, will love it when you don't forget them!