Need help deleting line from txt log

[00pavan00]

Hello i have Zero knowledge of PHP but unfortunately i need a small code as follow.

Let us consider i have list of names in a text log something called as file.log

That file.log contains the following data.

100.00
200.500
49.50
4.50
7.88

What i need is , i need a php code with a text box and captcha , when user enter a value in a text box for ex200.500) and need to give captcha after that need to click delete then that php script need to search that file.log and need to delete that line which contains that text(200.500), can some one please do it for me i already tried in internet becz of zero knowledge i am unable to understand it.

This is also for vbulletin ,its not for out of vbulletin.Thanku