Use enumeration to find the number of bit strings of length at most 4.

As shown in exercise 1.5, there are 14 bit strings of length at most 3. Adding the following sixteen bit strings of length 4:

1. \(0000\)
2. \(0001\)
3. \(0010\)
4. \(0011\)
5. \(0100\)
6. \(0101\)
7. \(0110\)
8. \(0111\)
9. \(1000\)
10. \(1001\)
11. \(1010\)
12. \(1011\)
13. \(1100\)
14. \(1101\)
15. \(1110\)
16. \(1111\)

gives us a total of 30 bit strings of length at most 4.