I think its hard to get the value from crosstab but one workaround would be.
- Create a shared variable in both subreports and assign the summary value to the shared variable.
Suppose cross tab is showing employee salary sum then in the formula assign the value to the shared variable as
Shared Numbervar report1;
report1:=Sum(employee.salary)
- similarly do in the second subreport aswell.
Now in main report create a formula
Shared NumberVar report1; Shared NumberVar report2; report1+report2;
let me know how it goes.