The merchant spent 30$ to buy the bag. 20% of this price is
![(20)/(100)\cdot 30=6](https://img.qammunity.org/2020/formulas/mathematics/middle-school/6fk51h9fyp62r46naacthfsgwod5s8w4xm.png)
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
![(90)/(100)x=36 \iff x=(3600)/(90)=40](https://img.qammunity.org/2020/formulas/mathematics/middle-school/siuqw6i37mbucgh6yb9iwhr9x3ethik1q3.png)
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.