In this task, you're given a passage, further information available on a particular linked term from the statement, and an answer term. Your job is to generate a question that can use the information provided to obtain the given answer. You should use the information on both passage and link information to create the question. Note that the answer to the question should be exactly the given answer, and if the answer is none, the answer to the question shouldn't be obtainable from the passage or linked information.

Passage: The 23 Special Wards of Tokyo were formerly Tokyo City. On July 1, 1943, it merged with Tokyo Prefecture and became Tokyo Metropolis with an additional 26 municipalities in the western part of the prefecture, and the Izu islands and Ogasawara islands south of Tokyo. As of October 1, 2015, the population of Tokyo is estimated to be over 13.4 million, or about 11% of Japan's total population. The latest estimate in 2019 shows the growing population of Tokyo with 13.9 million people, with the special wards 9.6 million, the Tama area 4.2 million, and the Islands 25,147. The prefecture is part of the world's most populous metropolitan area called the Greater Tokyo Area with over 40 million people and the world's largest urban agglomeration economy. , Tokyo hosted 51 of the Fortune Global 500 companies, the highest number of any city in the world at that time. Tokyo ranked third (twice) in the International Financial Centres Development Index. The city is home to various television networks such as Fuji TV, Tokyo MX, TV Tokyo, TV Asahi, Nippon Television, NHK and the Tokyo Broadcasting System.
Link Information: none Answer: none
How many people were living in the wards of Tokyo when it became Tokyo Metropolis?