Hi @Underdog 

1. Use a Web Service such as math.js web service

The site has some caveat - The duration per evaluation of this free service is limited to 10 seconds, with a maximum of 10,000 requests per day.

Let's say we want to calculate "1+2+3+4+5+6+7+8+9+10"

TIP: There is a Try it where you can enter your math expression and it will generate the URL

TIP: the '+' symbol converts to '%2B" 

STEP 1: Generate the Math Expression using the Build String action.

Put all the 28 values. Save to a strExpression

STEP 2: Replace '+' symbol with '%2B' using Replace Substring in String action.

Step 3: Configure the Call HTTP Web Service action

Address: http://api.mathjs.org/v4/?expr={Variable:strExpression} 

For this example, I used http://api.mathjs.org/v4/?expr=1%2B2%2B3%2B4%2B5%2B6

which is 1+2+3+4+5+6

Step 4: Run

If everything is configured correctly, it returns (using the Log)

Log to History 

Response Content returns 21

Cheers

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