Calculating only fields with check boxes 'Ticked'

I am completly new to creating custom scripting to calculate form fields, so please exuse my lack of knowledge.

I have a for where there is a table that the user of the form will enter (up to 24) values in one column. At the end of that column there is a total, I have been able to set this up fine using the basic calculations tool.

In this table however there is another column which has check boxes relating to each of the values added by the user in the previous column. This also has a total at the end of the column, this total is to be the sum of only the values where there are 'ticked' check boxes. Is this possible? (below is a screen shot if this helps).