so, a whole is 1. or 1/1 or 500/500 and so on.
the original price of this t-shirt was a whole price namely, 4/4.
the new price is 1/4 more than that, 4/4 + 1/4 = 5/4, and we know that's $85.
let's say "x" is the whole price, thus
[tex]\bf \begin{array}{ccll} price&fraction\\ \cline{1-2}\\ 85&\frac{5}{4}\\\\ x&\frac{4}{4} \end{array}\implies \cfrac{85}{x}=\cfrac{~~\frac{5}{4}~~}{\frac{4}{4}}\implies \cfrac{85}{x}=\cfrac{~~\frac{5}{4}~~}{1}\implies \cfrac{85}{x}=\cfrac{5}{4} \\\\\\ 340=5x\implies \cfrac{340}{5}=x\implies 68=x[/tex]
