Answer
Approximately $2$ years after $1995$.
Work Step by Step
Following the example, our equation is: $4.5=\frac{848t^2+3220}{115t^2+1000}\\4.5(115t^2+1000)=848t^2+3220\\517.5t^2+4500=848t^2+3220\\1280=330.5t^2\\3.87\approx t^2\\t\approx1.97$
(because $t$ cannot be negative)
Thus the sales were $4.5$ billion approximately $2$ years after $1995$.
