Regrouping data

[TGM™]

I have a macro which extract usable data and put them into excel. Problem arises when more identical data are extracted.
I'm looking for a macro to do the following in brief:

column C1 = A1+A26+A53 = "Nuclide"
column C2 = A2+A27+A54 = "H 1"
. . .
. . .
. . .

column D1 = B1+B26+B53 = " Activity"
column D2 = average(B2+B27+B54) = "0.00000E+00"
. . .
. . .
. . .
I have attached a sample file from the work extracted, thanks in advance.