Use TO_NUMBER on the prod_price column to convert from char to number to be able to multiply it with 0.25. Then use the TO_CHAR function (with formatting'$99, 999.00') to convert the number back to char.
Incorrect:
Not C: Use the formatting'$99, 999.00' with the TO_CHAR function, not with the TO_NUMBER function.
Note:
* Using the TO_CHAR Function
The TO_CHAR function returns an item of data type VARCHAR2. When applied to items of type NUMBER, several formatting options are available. The syntax is as follows:
TO_CHAR(number1, [format], [nls_parameter]),
The number1 parameter is mandatory and must be a value that either is or can be implicitly converted into a number. The optional format parameter may be used to specify numeric formatting information like width, currency symbol, the position of a decimal point, and group (or thousands) separators and must be enclosed in single
* Syntax of Explicit Data Type Conversion
Functions
TO_NUMBER(char1, [format mask], [nls_parameters]) = num1
TO_CHAR(num1, [format mask], [nls_parameters]) = char1
TO_DATE(char1, [format mask], [nls_parameters]) = date1
TO_CHAR(date1, [format mask], [nls_parameters]) = char1