The subscription to a popular magazine decreased from $66 per year to $52.80 per year.
The subscription is decreased from 66 to 52.80
Amount of decrease = 66 - 52.80 = $13.20
Percentage of decrease = decreased amount divide by initial amount
Percentage of decrease =

To find the percentage we multiply by 100
0.2 * 100 = 20%
20% of decrease for the magazine's subscription