I was told to always use the numbers after the period to represent the model number. From looking at your's, I'd say a straight stitch class 15 with drop feed. I don't know if there ever was a model 50 Kenmore.
If I started fixing Mama's sewing machine when I was 5 years old, I would have had my rear end warmed considerably. That was the age one of my brother's was when he started fixin all the doorknobs in the house.