$$30\times30\textbackslash\%+20\times 20\textbackslash\%=9+4=13$$ ounces.  $$13\div10\textbackslash\%-(30+20)=80$$ ounces. 
Amy mixes $$30$$ grams of a $$30\textbackslash\%$$ salt solution and $$20$$ grams of a $$20\textbackslash\%$$ salt solution together. How many grams of water should she add to the mixture to make it a $$10\textbackslash\% $$ solution? 
1. $$70$$ 
2. $$72$$ 
3. $$75$$ 
4. $$80$$ 