Percentages
The cost of the pair of earrings is $80 for the retailer. If it's sold at a 20% profit, then the price should be:
80 + 80 * 20 / 100 = 80 + 16 = $96
But the retailer wants to fake a 20% discount, so he must raise the price even more.
To make this last price 20% discount of the new price, it should be 80% (0.80) of that new price, thus we can calculate:
Final price = $96 / 0.80 = $120
Let's test our answer. The final price is $120, the buyer gets a 20% discount, thus the pays:
120 - 120 * 20 / 100 = 120 - 24 = $96
And this is exactly the price that gives us 20% profit on the original cost of $80.