How to do this question about money decreasing?

FV = PV x {1 + R}^N

5,800 =115,000 x {1 - 0.22}^N divide both sides by 115,000

0.0504347826 = 0.78^N Take the log of both sides

N =log(0.0504347826) / log(0.78)

N = ~ 12 Years to depreciate to about $5,800.