A very simple way to know the number of possible combinations in a binary number is given by the next formula:

Now, we should remember that an hexadecimal number contain 16 different digits, from 0 to F. Therefore

Thus, we will need 4 hexadecimal numbers to achieve the same values as a 16-bit number.
For the base-5 number we can do a similar procedure:

Therefore, we would need at least 7 numbers base-5 to achieve something similar to 16-Bit number