Thank you for contacting us. To display a summary calculated over a detail report in a master report, create a calculated field for a summary over a detail report's field using the Parent Relationship Traversal Operator ('^'). See Calculate an Aggregate Function. I have also attached a report definition and screenshot for your reference.
Please keep me posted of your results.
A similar question was discussed here:
XtraReports - How Sum Values of a Subreports in a Master-Detail Report.