Using the pairs given, we can compute how many countries are there(say, g) and how many people are there in each of these countries. In the above example, there are 3 countries, the 1st has 7 ppl, the 2nd has 2 ppl and the 3rd has just 1 person.

Since 2 ppl from diff. countries need to be sent, there are gC2 ways of choosing a pair of countries,in this case there are 3 countries, so 3 ways of choosing a pair of countries. Say, in one of these combinations, if countries i and j are chosen, then the no. of ways in which you can select the ppl from these 2 countries is (#of ppl in country i)*(#of ppl in country j), and this quantity is summed up over all the gC2 combinations.

In this case, with the 3 combinations being: choosing countries 1 and 2: 7*2 choosing countries 2 and 3: 2*1 choosing countries 1 and 3: 7*1

Summing it up, we get 23.