When you say you want to convert it to a hex number, do you mean that you want a string containing "98f9"? If you are not sure what that means then tell us what do you want to do with the hex number.
I want to convert both payloads to Hex and then combine both Hex numbers and convert to a decimal number
So If I can convert the payloads to Hex (resulting in C and 98FG) and combine these strings (resulting in C98FG) it is ok. After that the string containing the Hex number should be converted to a decimal value (end result 825593).