awk -F, 'NR==1 {  printf "%15s", $3
                         for ( i = 4 ; i <= NF; i++ ) { 
                             printf "%8s", $i 
                         }
                         printf "\n"
                         next
                      }                                               
                     {  ind[$3] = NF 
                         for ( i = 4 ; i <= NF; i++ ) {
                             result[$3,i] += $i 
                         }
                      }
            END {
                      for ( j in ind ) { 
                         printf "%15s",j 
                         for ( i = 4 ; i <= ind[j]; i++) { 
                             printf "%8d", result[j,i]
                         }
                         print line}
                   }' datafile