I think that you are asking how to sum the amounts from a subreport in the main report.
If so, shared variables is the answer. They typically come in groups of 3.
reset, typically in the group header
shared numbervar tot := 0;
"" //hides the output
increment (typically in the detail section, but for your case it might be in the subreport's report total):
shared numbervar tot;
tot := tot + {table.field} //for you it might be: tot := tot + sum({table.field});
""//again hide the output
display, usually in a group/report footer:
shared numbervar tot;
tot
HTH