According to the given question, let's calculate
To Calculate the Decrease Percentage, we can use this formula
= Percentage Decrease = [(Original Price - New Price)/Original Price] x 100
= [(180 - 81) / 180] x 100, where the Cost Price or C.P = 180 | Loss = 81
= (99/180) x 100 (Just for a Note $99 is the Selling Price or S.P)
= 55% is the Loss in %
Hope It's Simple and Easy to understand ;)