Question

Let's say you are standing on top of a mountain looking down at the valley below, where you can see cars driving on a road. You stretch out your arm, use your thumb to "sight" a car, and find that the car appears to be as long as your thumb is wide. Estimate how far you are from the car. Explain your method clearly. (You will need to make an assumption to solve this problem. Make a realistic assumption and make it clear what your assumption is.)