The population of a certain country is growing at a rate of 1.51.5​% per year. How long will it take for this​ country's population to​ double? Use the formula t equals StartFraction ln 2 Over k EndFraction commat= ln2 k, which gives the​ time, t, for a population with growth rate​ k, to double.​ (Round to the nearest whole​ year.)