Reuse accumulation field

[Kavita]

I have to do simple addition of two fields but i am facing issues in this in Libreoffice base reports. My requirement is to add like below

Group footer:
Value A (Accumulated sum of detail rows)
Value B

 Value C = Value A + Value B

I have tried instructions given in link but no luck. Please help me.

[Ratslinger]

Hello,

For your data field on the “Grand Total” try:

VALUE([AccumulationAmountSID] + [Tax])