STEP - BY - STEP EXPLANATION
What to find?
The price the retailer should marked them.
Given:
Cost per pair = $90
Sold at 10% discount
40% profit.
Selling price for 40% profit of the cost is;
[tex]\begin{gathered} 90+40\text{ \% of 90} \\ =90+36 \\ \\ =126 \end{gathered}[/tex]Let S be the price the retailer mark them.
[tex]S-10\text{ \% of S=126}[/tex][tex]\begin{gathered} S-0.1S=126 \\ \\ 0.9S=126 \end{gathered}[/tex]Divide both-side of the equation by 0.9
[tex]S=140[/tex]Hence, he need to mark them at the price of $140
ANSWER
$140