I don't

[Offroad]

Please, teachers...

Could you help me with this?

I was wondering which ones are right.

Someone asks
- Do you wanna do this?

Someone else replies

1) I don't whether/if you don't as well/too.
2) no, if you don't
3) I don't if you don't
4) could you suggest a better answer?

Many thanks

[David L.]

if the person is speaking in such a colloquial way as to say 'wanna' then
no, not if you don't
I don't if you don't
fit the occasion.
If you want to go the whole hog:
Nuh. Do you?

[Offroad]

Ok, I got it, David, thank you.

But if the person asks like this?

Do you want to do this?

What'd be the possible and formal answers?

Thank you very much.

[David L.]

"Not particularly, no. Do you?"