Answer:
Germany
Step-by-step explanation:
Tennis rackets are in a way, a luxury item that is only often bought by people who enjoy a middle-high, or high income. This is because Tennis as a whole tends to be an expensive sport to practice, since most tennis courts are located in private clubs, need to be rented for the practice, and the rest of the equipment associated with the sport: the footwear, and even the clothing, tends to be expensive as well.
For this reason, I would target a high income country first, and the most straightforward proxy to measure the average income of a nation is its GDP Per Capita, which is the GDP divided by the total population of the country.
According to the CIA Factbook, we have the following GDP Per Capita figures for the countries listed:
Brazil: $15,600
China: $18,200
Germany: $53,209
Italy: $38,200
Japan: $42,900
As a result, I would choose Germany, because it has the highest GDP per capita among the lot.