Stacked bar charts

[#1]

I'm trying to display some relatively straightforward sales data in the form of a stacked bar chart.  I've shown a rough example of my existing data below:

This is a combo chart with one dimension (sales month) and 4 expressions (actual sales [red], future order book [green], prior year [blue] and budget [yellow]).  I'm looking to keep things similar to the above, but need to try and stack the red and the green bars on top of each other (the red being actual sales and the green being the future order book).

Have tried various things, have googled quite a bit also but so far am struggling to achieve what I would have expected to have been relatively simple!  Can anyone offer any suggestions to help solve my problem??

Thanks