my understanding is that if there's a line, no matter how faint it is, that means you passed. if the cutoff point for the drug screening is 50 ng/ml like the at-home ones, you should be fine. although some companies like to screen their employees to as low as 15 to 20 ng/ml. as far as coke goes, doesn't that get out of your system in like 3 days to a week? i just remember all the hard drugs (no i don't consider weed to be a hard drug) getting out of your system faster.

to answer your question as to why the line was more faint than the other one; i have no idea. same thing happened to me. maybe you drank more that day and that's why the line was stronger? who knows.