I was given an electric Weedeater, model 307 with an 8" cut . The line is missing and I don't know how to replace it. I went to Lowe's and Walmart and found nothing for this model. Do I need a cartridge or just replacement string?

You can buy a preloaded spool or try winding your own string onto the old spool. There is a small slot or hole in the shaft right where the head is mounted. Insert a nail or screw driver into the hole and unscrew the knob on the spool.