The merchant spent 30$ to buy the bag. 20% of this price is
[tex]\dfrac{20}{100}\cdot 30=6[/tex]
So, he has to sell the bag at 36$.
This is not the selling price, but its 90%, because of the 10% discount.
So, the label price is such that
[tex]\dfrac{90}{100}x=36 \iff x=\dfrac{3600}{90}=40[/tex]
So, the merchant will declare a price of $40.
After the 10% discount, the price will drop to $36.
If she sells the bag for $36, her profit will be $36 - $30 = $6, which is 20% of 30 as required.
