Let n = the number of countries in North America.
2 n = number of countries in Europe
2 n + 7 = the number of countries in Africa

The total number of countries in all three continents is 122.

n + (2n) + (2n + 7) = 122

n = 23
So, there are 23 countries in North America.
Remember to find the number of countries in Europe and Africa.