Working together: $$2000\div10=200$$ envelopes per hour.  Tom: $$200-120=80$$ envelops per hour, $$2000\div80=25$$ hours. 
Tom and Jerry have to mail $$2000$$ envelopes for a new marketing campaign. Jerry can mail $$120$$ envelopes per hour. With Tom\textquotesingle s help, they can get the job done in $$10$$ hours. How long will it take Tom to finish the job by himself? 
Options:
[1] $$24$$ 
[2] $$25$$ 
[3] $$30$$ 
[4] $$80$$ 