For the first term, \(a = \frac{-108}{r^2} = \frac{-108}{\left( \frac{-2}{3} \right)^2} = -243\).
The sum to infinity is given by \(S_\infty = \frac{a}{1-r} = \frac{-243}{1 - \left( \frac{-2}{3} \right)} = \frac{-243}{\frac{5}{3}} = \frac{-729}{5} = -145.8\).