Sum of an column for an entire report? (access)

I have a crosstab query for a service record that gives the downtimes of specific location in my mill (Quad, Twin and Canter) Ive broken it down like this

Code:

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Date | Shift | Department | Total of Downtime | Canter | Quad | Twin
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I got that working fine but I want totals of the last 4 columns at the end of the report, and I'm at a loss of how to to that... I tried putting text boxes in the report footer that was =Sum([X]) where X is Total, canter, quad and twin but I get an #error when I run the report.

Help would be appriciated.