The solution;
[tex]\begin{gathered} \text{Cost of sofa=259} \\ \text{Tax paid=8\% or 0.08} \\ \text{Amount of tax=259 x }0.08 \\ \text{Amount of tax=20.72} \end{gathered}[/tex]By buying the sofa in Oregon, Rodrigo would have saved $20.72
Thats the amount he would have paid as tax after the actual cost which is $259.
That is, the cost in Washington would have been $279.72