During a sale, the original price of a garment is lowered by 20%. Because the garment did not sell, its sale price...

In questions dealing with percentages, it is helpful to start with 100 as the initial number

Let us assume original price was 100
During sale it's lowered by 20% -> so price becomes -> 80
Now, it was further reduced by 10%. This 10% is of the current price, and not original price.
So new price -> 80 - (10% of 80) = 72
Now the question asks, what percent of discount could have been applied on the original price (100) to get directly to the latest price (72)
Answer is easy -> 100 -72 = 28