Every ten years, the Bureau of the Census counts the number of people living in the United States. In 1790, the population of the U. S. was 3.93 million. By 1800, this number had grown to 5.31 million. Write an exponential function that could be used to model the U. S. population y in millions for 1790 to 1800. Write the equation in terms of x, the number of decades since 1790.