A car is moving along Highway 20 according to the given equation, where $x$ meters is the directed distance of the car from a given point $P$ at $t$ hours. Find the values of $t$ for which the car is moving to the right and when it is moving to the left. Draw a diagram to describe the motion of the car.
motion of car: $x = 2t^3 + 15t^2 + 36t + 2$
So when $x$ is positive it moving right and when $x$ is negative its moving left?