The World's Billionaires

Columns: No | Name | Net worth ( USD ) | Age | Nationality | Source ( s ) of wealth
1 | Bill Gates | $ 79.2 billion | 59 | United States | Microsoft | 2 | Carlos Slim | $ 77.1 billion | 75 | Mexico | América Móvil , Grupo Carso | 3 | Warren Buffett | $ 72.7 billion | 84 | United States | Berkshire Hathaway | 4 | Amancio Ortega | $ 64.5 billion | 78 | Spain | Inditex | 5 | Larry Ellison | $ 54.3 billion | 70 | United States | Oracle Corporation | 6 | Charles Koch | $ 42.9 billion | 79 | United States | Koch Industries | 6 | David Koch | $ 42.9 billion | 74 | United States | Koch Industries | 8 | Christy Walton | $ 41.7 billion | 66 | United States | Walmart | 9 | Jim Walton | $ 40.6 billion | 66 | United States | Walmart | 10 | Liliane Bettencourt | $ 40.1 billion | 92 | France | L'Oreal

Example questions:
How old will the Spanish Billionaire in 2015 ranking be at the end of this year ? | How many years ago did the 70 year old Billionaire retire in 2015 ranking ? | Which Billionaire in 2015 ranking associated with Walmart is older ? | What city was the richest 2015 Billionaire born in ?

Answers:
84 | 2 | Jim Walton | Seattle