Max Value Across Specific Columns, By Row

Hi,

I have a table that show total sales by SKU, and splits out sales per week for the previous four weeks.  I would like to insert a column at the end that shows the figure from the best-performing week from the Week 1-4 columns for each SKU.  I know this would be simple for a cross-tab table but my data isn't suitable for this layout.

Thanks,

Jamie.