3-4 weeks Urine or Hair

This is my situation, I have approximately 3-4 weeks before pre-employment testing at a new job. I'm a light smoker 3 hits per night Fri, Sat, Sun and rarely during the week. I'm 190lbs, 5'11", 39 yrs.. I'm not sure if this will be a urine or follicle test. I see kits available from Detox online raging $90-$100 for both tests, if it works i have no problem spending the money. The problem is i see so many products but what will work in my situation. I believe there is also a probationary period, so what and how long should i take a product before my system is totally clean. Oh yea, and i smoked today:).

Been lurking here for a while and you guys give really great advise, Thank You!