Necessity is the Frank Zappa and the Mothers of Invention...

My co-workers have just discovered that I can "really" sew. I was approached by a lady at work with a look of desparation on her face: "June, I've done something terrible! I ruined 2 pairs of slacks trying to alter them myself!"
"Okay, what exactly did you do?" ( thinking, how bad could it be?)
"I cut them off and used glue to try and hem them and now they are too short!"
Gulp. Okay, do I want to tackle this?
"Okay, bring them to me tomorrow. Do you still have the pieces you cut off?"
Yes, she did. Oh boy, she was right- a BIG mess.
I have never ever faced a hem on a pair of pants, but here goes nothing! Eeek. Nothing ventured, nothing gained.
First, I took out the hem of the sliced-off pieces and trimmed the pieces down to a seams-width where I would be joined them back to the raw hem edge. I could use the serged edge of the hem-piece to save some time and trouble.

Next, I joined the pieces to the raw edge of the pants, trying to keep the hem-piece even. The bottom of the pants was so uneven that I had to ignore what was underneath- just keep the seam on top straight and smooth.

See what I started with? Notice the glue....

I joined the pieces together, easing the pieces to fit as best I could. Then I understitched so the facing would turn under more easily.