well, the numeric difference will be 136 - 80 = 56, now, if we take 80 (original price) to be the 100%, what is 56 (the increase) in percentage off of it?
[tex]\begin{array}{ccll} amount&\%\\ \cline{1-2} 80&100\\ 56&x \end{array}\implies \cfrac{80}{56}=\cfrac{100}{x}\implies \cfrac{10}{7}=\cfrac{100}{x} \\\\\\ 10x=700\implies x = \cfrac{700}{10}\implies x = \stackrel{\%}{70}[/tex]
