A certain car brand estimates that a certain model, that now costs 21000 euro, will devaluate 5% per year.
How much will this car cost in 6 years?
$$21000 \cdot (1+.05)^6 \approx 28142$$
Now I remove the initial value from this one to get the compound devaluation
$$28142-21000 = 7142$$
Then I subtract this value from the initial value
$$21000-7142 = 13858$$
But my book says the solution is 15,437 euro.
What did I do wrong?