The Average Number of Vehicles Waiting in Line at a Toll

The average number of vehicles waiting in line at a toll booth of a super highway is modeled by the function $n(x) =\frac{x^{2}}{0.5(1-x) }$ , where $x$ is a quantity between 0 and 1 known as the traffic intensity. To the nearest tenth, find the average number of vehicles waiting if the traffic intensity is 0.81 .

A) 6.9 vehicles
B) 1.6 vehicles
C) 3.5 vehicles
D) 8.5 vehicles