In 1987, the population of country a was estimated at 87 million people, with an annual growth rate of 2.7%. the 1987 population of country b was estimated at 243 million with an annual growth rate of 0.6%. assume that both populations are growing exponentially. (round your answers to the nearest whole number.) (a) in what year will country a double its 1987 population?

The annual multiplier of the population is 1 +2.7% = 1.027. So, after x years, the population is multiplied by 1.027^x. You want to find the value of x that makes this multiplier be 2.
  2 = 1.027^x
  log(2) = x*log(1.027)

Then, at a growth rate of 2.7%, the doubling time of the population is
  x = log(2)/log(1.027) ≈ 26.02 . . . . . . the number of years after 1987

The population of Country A is expected to be double its 1987 value in the year 2013.