Apply the rule of 70 to solve the following problem. Real GDP per person in Mexico in 2005 was about $12,000 per person, while it was about $48,000 per person in the United States. If real GDP per person in Mexico grows at the rate of 10 percent per year, how long will it take Mexico's real GDP per person to reach the level that the United States was at in 2005? (Hint: How many times would Mexico's 2005 real GDP per person have to double to reach the United States' 2005 real GDP per person?)