To make the total of R54 + R61 + R63 you can use this code:
{{ $7+$8+$9 | currency }}
To calculate the sum of the registers you created ($7, $8 and $9) the + sign needs to be inside the brackets.
If you then want to create a result tag for this total to use it in another template you can add this code:
{% result 'totaal' $7+$8+9 %}
Hope this was what you were looking for!
For future reference, you can find a guide here on how to paste your code correctly in a community post.