use to_number to convert char to number

 
SQL>
SQL>  select to_number( '15' )
  2      from dual
  3    /
TO_NUMBER('15')
---------------
             15

1 row selected.

SQL>
SQL>
SQL> --

1.	Convert the string to a number and pass the format string $99,999.99 to TO_NUMBER()
2.	Convert string to a number and then adds 25.5 to that number
3.	Converts the string 970.13 to a number using TO_NUMBER()

use to_number to convert char to number : TO_NUMBER « Data Type « Oracle PL / SQL