The serial number will tell the tale. The vintage Trek site will tell you how to figure which model this is based on the serial number.
This is not a 720 as that is a touring bike with cantilevers other than in 1982 when it came with caliper brakes.
Given the parts group and color, I'd guess an '83 620.
Last edited by bikemig; 02-26-20 at 11:11 PM.