What you are showing is numbers in "numeric-edited" format, the sort of thing that might be used for a line on a printout.
If that is the format your data is in, you can't directly use the "numbers" for arithmetic operations. If you have been told there are numbers on a file, which are signed and with two decimal places, your actual PIC could be S9(3)V99, where S is an implicit sign and V is an implicit decimal place (the sign will acutally be stored in the data, but not by "displacing" a digit, so the length of the field won't change, the decimal point is purely implicit, with the compiler generating the correct code from the definition, but nothing stored on the file).
In your example, you could define the sign as being SEPERATE but there is nothing you can do about the decimal point. So, +12345 could be defined as 999V99 SIGN SEPERATE and be treated as positive 123.45 and used in arithmetic.
It is well worth spending some time with the manuals and constructing some examples so that you become familiar with all this, you learn much better that way than just by being told. Definining the data correctly will save you problems in the future, and even improve your code in the PROCEDURE DIVISION.