First of all, let's convert all the measures to the same unit: 4 feet are 48 inches.
Now, as the wheel turns, there is a proportion between the angle and the distance travelled: for example, when the car moves forward a whole circumference, the angle will be 360°. Conversely, if the wheel turns 180°, then the car will move forward a distance which is half the circumference of the wheel, and so on.
Since the radius is 16 inches, the circumference will be
So, we have the following proportion:
that you can read as: "if an angle of 360 corresponds to a distance travelled of , then the unknown angle x corresponds to a distance travelled of 48 inches.
Solving for x, we have