1. The problem statement, all variables and given/known data The population of a country is growing exponentially. The population in millions was 120 in 1970 and 150 in 1980. (a) What is the population t years after 1970? (b) How long does it take the population to double? (c) When will the population be 400 million? 2. Relevant equations 3. The attempt at a solution I don't know how to start the equation, so I listed out the years and the populations to no avail.