Assume that a "leader country" has real GDP per capita of $40,000, whereas a "follower country" has a real GDP per capita of $20,000. Next suppose that the growth of real GDP per capita falls to zero percent in the leader country and rises 7% in the follower country. If these rates continue for long periods of time, how many years will it take for the follower country to catch up to the living standard of the leader country?