A Public Class In Sub-folder Is Not Getting Found By Another Class While Compilation

I was doing coding exercise from a book ('OCP Java SE 6 - Practice Exams' by Kathy Sierra and Bert Bates). I came to a question that told to demonstrate the difference between 'default' and 'protected' access rules by creating/making a directory structure and putting a couple of classes in different packages.

For this, I made a total of four classes, out of which, three classes are-Car, TestingCars, CarDimensions. (The fourth is not yet used in testing code till now, so, I am giving only the other three classes.) Their coding is given below.

Out of these classes, the classes- TestingCars and Car - are in a directory (say, FolderName). And, the class- CarDimensions is in FolderName's sub-folder.

The class 'CarDimensions' is public (and its components too are public). And, I am testing all the classes from the class- 'TestingCars'. But, this class (TestingCars) is not able to find the public class- 'CarDimensions' which is in its sub-folder and gives two 'Cannot find symbol' errors citing the class-CarDimensions. Also, If all three classes are put in one single directory, the programs work, without any error.

Coding:
Class TestingCars:class TestingCars {
public static void main(String[] args) {
Car c = new Car();
c.setType("FourWheeler");

[Code]....

I could not find why the public class- CarDimensions- is not getting found by the TestingCars class.