Help with Debugging

[Sherri]

I am having problems debugging this program. It keeps saying there's an error in line 
5 near '('

Here's the code:

#!/usr/bin/perl -w
#This program replaces cm398p with cm498p
use strict;
@Classes = ("cm140", "cm325", "cm398p");
subreplace
{
use $ref -> [X] = "cm498p"
}
replace (/@Classes);
print @Classes;

Please help. Thank you.