You can’t apply a TO_CHAR() function to an argument with CHAR data type because 10-JAN-16 is already a CHAR literal. It will generate an error
You can’t apply a TO_DATE() function to an argument with DATE data type because date_of_birth is already a DATE. It will generate an error
But, you can apply TO_NUMBER() function for NUMBER data type. It will work, see below.
You have to remember these rules. Conversion functions are tested heavily throughout the exam