Generic exponential growth model: y = Ao[1+r]^t
In this case: r = 6.2% = 0.062
y = 2Ao .....[the double of the initial value]
Then: 2Ao =Ao (1 + 0.062)^t
(1.062)^t =2
Take logarithm to both sides
t ln(1.062) = ln(2)
t = ln(2) / ln(1.062)
11.1789
Hence, the population doubles in 11.18 days