How to create this formula in VB or Conditional Formating: If Column A = 3 Days before Column B, Then Highlight red.

Hi,

I would like to create a formula in excel that allows me to do this  

If Column A = 3 Days before Column B, Then Highlight red.

I don't think Conditional formating allows me to do this.

Please advise.

Thank you.

Regards,

Joshua Tay