I have the following script

awk '$1 ~ /^[A-Z]*[0-9]+/ {
        s += $NF;
        m++
    }
    END {
        print NR, m, s
}

awk '$1 ~ /^[A-Z]*[0-9]+/ ... search for lines where the first field is either letter(s) followed by number(s) or only number(s)
s += $NF; ...add the value of the last field to variable s
m++ ... post increment counter m
}
END {
print NR, m, s ...print the number of fields, the value of the counter and the value of variable s (which is the sum of matching fields)
}

Why do you get 9 and not 8 records? Most likely beacuse the file ends with a blank line.

The + means one or more occurrences of the previous term in the regular expression.

Can you explain me which symbol implies "or only number" 'cause I think that drove me in the wrong results

[A-Z]* , the * means zero or more occurrences.

Thanks a lot for your help

Sorry but still I have a question.
With your explanation it shouldn't count the line with the empty field $1 (it was misstyped and couldn't been seen the <tab> so the line was <tab> 6) and the R2D2<tab>3. But it count's them. Why?