Step 1 – Select Value Rules and the select the rule with “value =”
Step 2 – Select Number Fields and select the expression with 2 variables and a “+” between them. Repeat for the number of additional variables that you need. For example, if you are creating a sum of 3 numbers and then wanting to subtract a 4th number, drag this expression over to your rule 3 times and connect them into a succession of expressions.
Step 3 – Click on the drop downs to choose your fields and operands.