Help with a ladies Rolex

[Levack]

I have a ladies Rolex that was given to me. It could be up to 75 years old but still is in working condition. It appears to be stainless steel, says "Rolex" and "Swiss made" on the face. On the back the best I can make out is the number 7842 1385 on two lines. There may be another "mark" between the "8" and the "4" in the first set of numbers. I have not opened it up and have not been able to find a picture of this watch on any site. I would appreciate anyo info possible regarding history and value.

Rick