Need info on homelite ut20556B string trimmer st-145---just purchased used trimmer. Would appreciate info on gas / oil mix ratio & string replacement info. Did not have a manual. Thank you.

Try this site to download a manual and it will tell all you need, I think its 16:1 for the gas. Owner's Manual | Find Product User Manuals - Managemyhome.com

If you go to homelite.com put in your model number it will give you specs.