I figured it out
racket -it filename.rkt
> C
3
or
racket -iu filename.rkt
> C
3
Not really sure what the differences are, but the command line help says the following
-t <file>, --require <file> : Like -e '(require (file "<file>"))' [*]
-u <file>, --require-script <file> : Same as -t <file> -N <file> --
-N <file>, --name <file> : Sets `(find-system-path 'run-file)' to <file>