The cynical answer is about 7-15: themselves, their family and close friends. Or at least thats how it appears in the US given how little we do about it, even though we (half) give it plenty of lip service.
What kind of question is that? Do you seriously expect me to give an "exact" solution? Furthermore how many complicated issues have solutions that have no potential to cause harm and are guaranteed to help. I think it is pretty clear at this point that there is no magic solution to climate change and we have to make some collective sacrifices. Individually I did make a "sacrifice" by going vegan. After 3 years I haven't noticed any harm and I'm confident it has helped about epsilon amount. I guess that fits your criteria.