Question: A developing country gross domestic product (GDP) from 1988 to 1999 is approximated by the function \(G\left( t \right)=-0.1{{t}^{3}}+1.2{{t}^{2}}+60\), with \(0\le t\le 11\), where \(G\left( t \right)\) is measured in billions of dollars and t = 0 corresponds to the year 1988. Find the year the growth rate of the country was maximal.