$$10\times20\textbackslash\%+40\times 25\textbackslash\%=12$$ grams.  $$(10+40)-12\div40\textbackslash\%=20$$ grams. 
Amy mixes $$10$$ grams of a $$20\textbackslash\%$$ sugar solution and $$40$$ grams of a $$25\textbackslash\%$$ sugar solution together. After~\uline{~~~~~~~~~~}~of water evaporates, the percent concentration of solution is $40\textbackslash\%$. 
Options:
A: $$15$$ grams 
B: $$18$$ grams 
C: $$20$$ grams 
D: $$25$$ grams 