Excel Formula Advice for CO2 Calculations

I am putting a report together on carbon emissions that requires use of the following equation attached (apologies Insert Image function would not work) that allows 1990 targets to be converted to 2005 equivalents. I would greatly appreciate guidance on how this would be applied to Excel formula. For background the full blog that contains a working example is provided at the following link http://www.carbondescent.org.uk/blog/?p=238

Thanks in advance for any advice.