Remember:
\[
\boxed{
\begin{aligned}
&\text{Williamson synthesis: } \mathrm{RONa+R'X\rightarrow ROR'},
&\text{HI/HBr cleaves ethers at the tertiary carbon by }S_\mathrm{N}1,
&\text{and at the methyl/primary carbon by }S_\mathrm{N}2.
\end{aligned}
}
\]