say the original price is "x", and therefore is the 100% of the price, however Belk's is having a sale and the pants were 20% off, therefore 12.50 is really just 100% - 20% or 80% of the original price.
now, we know 12.50 is the 80%, and "x" is the 100%, what the dickens is "x" anyway?
[tex]\bf \begin{array}{ccll}
amount&\%\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
12.50&80\\
x&100
\end{array}\implies \cfrac{12.50}{x}=\cfrac{80}{100}\implies \cfrac{12.50\cdot 100}{80}=x[/tex]
