Because, salt was needed to flavor food, preserve meat, used for medical purposes, and to keep the body healthy. But in West Africa, salt was rare. So, West Africans traded their gold for salt. Salt was so valuable, it was worth its weight in gold. 1 pound of salt = 1 pound of gold. How amazing.
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Answer:
In 1949, the prospect of further Communist expansion prompted the United States and 11 other Western nations to form the North Atlantic Treaty Organization (NATO). The Soviet Union and its affiliated Communist nations in Eastern Europe founded a rival alliance, the Warsaw Pact, in 1955. The alignment of nearly every European nation into one of the two opposing camps formalized the political division of the European continent that had taken place since World War II. This alignment provided the framework for the military standoff that continued throughout the Cold War.
assuming efficiency of each man to dig trench, in one day, for one hour is constant,

so one man, working for one hour in one day can dig 1.5 m
so 8 men, working 3 hours a day and will take, say $d$ number of days and efficiency will be constant. so,
$\frac32=\frac{220}{8\times3\times d}$
$\implies d=\frac{55}9=6.12$