Shell Programming and Scripting

$ cat file
x A 10 20 30
x B 5 10 12
x C 10 4 5
x D 10 3 6
x K 10 23 4
x M 5 7 0

x A 15 30 42
x C 20 7 11
x K 15 30 4

$ awk '
{ for (i=3;i<=NF;++i) sum[i]+=$i; j=NF}
END {for (i=3;i<=j;++i) printf "%s%s",OFS,sum[i]}' file

 50 67 57

!(FNR % 2) {
     printf("%s%s%s%s", f2[1], OFS, f2[2], OFS);
     for (i=3; i<=NF;i++)
        printf("%d%c", $i + f2[i], (i==NF) ? RS : FS)
     split("", f2)
     next
}
{
  split($0, f2)
}