so, the tax which is 77% of the price is 34.16, so say the futon is "x" worth.
so, "x" is the 100%, and we know that 34.16 is the 77%, what's "x"?
[tex]\bf \begin{array}{ccll}
amount&\%\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
x&100\\
34.16&77
\end{array}\implies \cfrac{x}{34.16}=\cfrac{100}{77}\implies x=\cfrac{34.16\cdot 100}{77}[/tex]