selection based on previous selection output

[#1]

Please refer the Excel file For Install Complete(i.e([ Plan step description=[Install] and [Plan step Actual End date] corrensponding to Install is present   )

                  If( ([ Plan step description=[Warranty Start] and [Plan step Actual End date]  = Null) then days =

                                                             Today()- { aggr ([ Plan step description=[Installation] ),  [Plan step Actual End date] ,UTID }one

Can anyone help me to find Days in term  of UTID