How do I lose 40lbs and still keep my butt and boobs?

I need to lose 40 more lbs, I've already lost 20lbs and I noticed that I'm losing it mostly in my butt and boobs.

Are there any exercises to help me keep my butt and boobs ?

would building muscle help me keep them ?

How do I lose 40lbs and still keep my butt and boobs?
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