well, the original price was "x", which oddly enough is the 100%, we also know that 25% off that is 30 bucks, so namely 100% - 25% = 75%, is 30 bucks, so
[tex]\begin{array}{ccll} amount&\%\\ \cline{1-2} x&100\\ 30&75 \end{array}\implies \cfrac{x}{30}=\cfrac{100}{75}\implies \cfrac{x}{30}=\cfrac{4}{3} \\\\\\ 3x=120\implies x=\cfrac{120}{3}\implies x=40[/tex]
