jmc

We have $$\begin{array}{rl}20(25)+10(10)& =10(25)+n(10)\\ 600& =250+10n\\ 35& =n⟹\boxed{\text{D}}\end{array}$$ The $n$ dimes' values need to sum to $10$ quarters and $10$ dimes.$$10n=10\cdot 25+10\cdot 10$$ we can divide both sides by $10$. $$n=25+10=35$$ So, our answer is $\boxed{35}$----stjwyl