Add all values in a Storyline 360 table column?

Do you want the user to enter the seat time during development? If so, put Numeric Entry Fields in each row. 

When you insert an entry field, Storyline automatically creates a variable to hold its value.

• I suggest you rename each variable (e.g., "Row1," "Row2," etc.) 
• Note that the value doesn't change until the field "loses focus" (that is, the user clicks something else). Therefore, it's best to have a button (e.g., "Done") for the user to click when they're ready for the values to be added. 
• This button can also be used to run the triggers for adding the values.

You'll need create a number variable (e.g., "Total") to hold the final total.

Add triggers to the "Done" button that add the value of each row variable to the "Total" variable. For example, those would look something like this: 

Finally, wherever you want to show the total, insert a reference to the "Total" variable. 

Here's more info about about data-entry fields: https://community.articulate.com/series/articulate-storyline-360/articles/articulate-storyline-360-user-guide-how-to-work-with-data-entry-fields 

And here's more info about variables: https://community.articulate.com/series/articulate-storyline-360/articles/articulate-storyline-360-user-guide-how-to-work-with-variables 

And if you don't want the user entering the values, well, just enter the values. You could show the total elsewhere by just entering the total. There's no need to bother with variables if you can do the math in advance.