Let the rate of increase be \(r\%\). According to the question: \[ 13310\left(1 + \cfrac{r}{100}\right)^3 = 17280 \] \[ \Rightarrow \left(1 + \cfrac{r}{100}\right)^3 = \cfrac{17280}{13310} = \left(\cfrac{12}{11}\right)^3 \] \[ \Rightarrow 1 + \cfrac{r}{100} = \cfrac{12}{11} \Rightarrow \cfrac{r}{100} = \cfrac{12}{11} - 1 = \cfrac{1}{11} \Rightarrow r = \cfrac{100}{11} = 9\cfrac{1}{11} \] Therefore, the population growth rate is \(9\cfrac{1}{11}\%\).