To calculate at what percentage is increasing or decreasing the function, we can make a value table:
So, to calculate the increasing or decreasing percentage, you have to:
1. Subtract the starting value by the next value
2. Divide it by the starting value
3. Multiply it by 100
[tex]\frac{20588-20642}{20642}\times100=-0.26[/tex]Because it's a negative percentage we know that it's decreasing by a 0.26% each year.