$$40-40\times25\textbackslash\%\div40\textbackslash\%=40-25=15$$ ounces. 
Bowen has $$40$$ ounces of a $$25\textbackslash\%$$ sugar solution. After~\uline{~~~~~~~~~~}~of water evaporates, the percent concentration of the solution is $$40\textbackslash\%$$. (Evaporate: the water turns from liquid into vapor and is no longer in the solution anymore.) 
Options:
1) $$15$$ ounces 
2) $$12$$ ounces 
3) $$9$$ ounces 
4) $$6$$ ounces 