This can function like a simple interest problem because there's a principal ($300), a rate (20% decrease or -0.2 as a decimal each year), and a time (4 years).
I = Principal x rate x time = (300)(-0.2)(4) = -240In 4 years, the PDA loses $240 worth of value. So it has a $60 value now (300 - 240).
NOW, that's assuming that the percent decrease is based on the $300 every year. If the percent decrease is based on the value each year, then it's different.
