The problem is really at line 662, not 641. It is the extra "Real(" on that line.
The reason that the line number is reported incorrectly is that the PG translator is stripping out blank lines before BEGIN_TEXT and after END_TEXT before processing the code, but it uses the original PG file in the error output. That means the line numbers don't match up between the error message and the listed code.
I have modified the PG Translator to not remove the blank lines, and that should make it report the proper error lines in the future. You will need to get the latest version of /pg/lib/WeBWorK/PG/Translator.pm for that.