Hi Susan - a few ways:
Extend command will let you make it longer interactively if you bypass the select Boundary prompt - start the command with no selection.
Connect will extend two (coplnar) lines to meet each other.
Turning on points and moving them - with SmartTrack active will be the easiest, probably.
Scale1d from one end.
Gumball one end point (f10- PointsOn) with Gumball set to align ‘by object’.