I'm not Bunuel/Karishma, but I can try to help you. I don't think that it is 700+ problem. You even don't need any equations. Just be accurate with percents.
Since the problem doesn't depend on the number of birds in reserve you can suppose that there are 100 birds.
From them 100*0.3=30 are Hawks.So, there are 70 non-Hawks.
There are 0.4*70=28 Paddyfield-Warblers. Therefore, there are 0.25*28=7 Kingfishers.
The total number of birds in the nature reserve that are not Hawks, Paddyfield-Warblers, or Kingfishers is 100-30-28-7=35.
The answer is B.
Hope this helps.
I'm happy, if I make math for you slightly clearer
And yes, I like kudos:)