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.
┬а 2 = 1.027^x
┬а log(2) = x*log(1.027)
Then, at a growth rate of 2.7%, the doubling time of the population is
┬а x = log(2)/log(1.027) тЙИ┬а26.02 . . . . . . the number of years after 1987
The population of Country A is expected to be double its 1987 value in the year 2013.