A central feature of the white community in Rhodesia was its transience, as white settlers were just as likely to leave Rhodesia after a few years rather than permanently settle; for example, of the 700 British settlers who were the first white settlers, arriving in 1890, only 15 were still living in Rhodesia in 1924. As the white population of Rhodesia had a low birth rate (18 per 1,000 compared to the African rate of 48 per 1,000), to maintain white population growth was largely dependent upon taking in new white immigrants with immigration accounting for 60% of the growth of the white Rhodesian population between 1955–72. However, the American historian Josiah Brownell noted that the turnover rate for white residents in Rhodesia was very high, as Rhodesia took in a total of 255,692 white immigrants between 1955–79 while the same period a total of 246,583 whites emigrated. Even during the boom years of the late 1950s, when Rhodesia took in an average of 13,666 white immigrants per year, mostly from the United Kingdom and South Africa, an average of about 7,666 whites emigrated annually. Between 1961–65, Rhodesia took in an average of 8,225 white immigrants per year while also having an average white emigration of 12, 912 per year. Many prospective white immigrants in Rhodesia arrived seeking economic opportunities and departed with fluctuations in the security situation as the Bush War intensified. A substantial number were uninterested in settling there permanently and did not apply for Rhodesian citizenship, despite a much-publicised 1967 campaign urging them to do so. Brownell asserted that patriotism in the white community was "shallow" due to its essentially expatriate character. Brownell also claimed that the majority of white immigrants in the late 1960s and early 1970s were unskilled laborers who competed with the countrys black African workforce and did not contribute badly needed technical or professional skills to the country. He argued that this was due to a government policy aimed at making white immigration as "unselective as possible" and guaranteeing every white immigrant a job.
Question: How many more, per 1000,  was the birth rate in Africa than the white population of Rhodesia?
Answer: 30