A stated in the previous post, the '7" is probably the frame manufacture year, which would make it 1997 or 2007. Given the level of the bicycle and the presence of a suspension fork, I would also suspect 2007. The rear derailleur appears to be a Shimano Tourney TX series with the large pulleys, which would fit this time frame. There will be a two letter date code on the back of the derailleur which you can use to date it, using the information on the components page of the Vintage-Trek website. Let us know what you find. BTW, welcome to the forums.