Country A is growing at a constant rate of 2 2% per year, while country B is growing at 4% per year. However, the current GDP level in country A is $100 billion and in country B it is $50 billion. How long it will take for country B to catch up with country A? (Hint: use the rule of 70.)
1) 20 years
2) 10 years
3) 40 years
4) 35 years