Summation box from dropdowns

There must be a reason your form is performing poorly which may not be solved by switching from checkboxes to dropdowns.  This article might help you improve the performance.  To add up specific selections from the dropdowns you would have to loop through the fields.  You should use a numbering system to name them to make this easier.  For example, if you create the first dropdown in a series and name it "Dropdown", then in form editing mode, right-click > Create multiple copies, then enter 25 down and 1 across you will end of with 25 fields named "Dropdown.0" through "Dropdown.24".  In the summary field for "FOC" enter the following custom calculation script:

var ttl=0;
for(var i=0;i<25;i++)
{
if(this.getField("Dropdown."+i).value=="FOC")
{ttl++}
}
event.value=ttl;

If your fields are not named with a numbering system you would have to create an array of field names and loop through them instead.

How many dropdown fields you have, and what are the names?

You want to result show in separate fields for each selection?