how long does darvocet 100 stay in your system?

just had a drug test for work and had taken a few for back pain that my mother had in the medicine  chest.  I have stomach problems and drug interaction problems with most other medication for pain and was authorized by dr to take them.  Drug test people didnt like that.  Please give me an idea of how long they will be in my system- i am a large woman, semi active, 48 years of age.