Can somebody help me to write PHP function ? - Just in Time alghoritm.

Hi, I have verry big problem.
I must write function using dates.
This is a problem:
I have some dates for example: 2006-01-01, 2006-02-05, 2006-10-15 etc.
then some times: 20sec, 50sec, 45sec etc
and some quantity of parts: 200, 300, 240
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I must sort dates,times and quanties, then I must calculate:for ex.
2006-01-01+200*20, etc. and then add next date+quanntity*time. Please
HELP me.

It's like "Just In Time" alghoritm.


Thanks for All.