Suppose economies A and B have the same initial level of GDP per capita at $15,000, and each economy begins with a constant growth rate of 1 percent per year. (Neither country has good institutions for economic growth at first.) Then Country A enters an era of political stability, establishes property rights, and installs incentives for entrepreneurship. Country A's economic growth rate consequently improves to 5 percent. Assuming population growth rates remain unaffected, how much longer will it take Country B to double its per capita GDP level compared to Country A?