Problems using the "IF" formula

How to ask the question and keep it simple. I am no expert using excel and struggle with the easiest of formulas but need assistance using the "IF" command. I have a works spreadsheet which is used by employees to keep track of their leave allocation but it needs finalised so that employees know exactly what leave they have left at the end of the day. I'll keep all info as easy as possible.
1. Column E = No of hours this request
2. Column F = No of hours left to take
3. Column G = Approved (requires a YES/NO response from management)
Providing Approved (Col G) = Yes, I can get column F to show the correct number of hours left (F - E). My problem is when the approved column = NO. Column E is still subtracted from column F giving the impression that the employee has used more hours than he actually has. I require a formula that will prevent hours being deducted if the Approved column returns a NO response
I hope someone out there is following what I am trying to achieve because I am now totally confused
Operating system is Windows 7
Microsoft office version 2007
Please try to keep any response DEAD simple because like I said, I'm an idiot when it comes to excel

Regards
warrantX1145