Create a calculation field like below
The calculation will give the value like below
((15853-11996)/11996)*100 = 32.15
Drag it to Under Sum(Values) in measure values section you can see the value of 32.15 for Theresa
Hope this helps kindly mark this answer as correct or helpful so that it will help others
Naveen B' s answer will give you what you want. But I understand the usage of table calculations and Lookup functions from his answer might feel complicated.
You can use the following approach, for simpler understanding.
Assuming you want to compare how all the other groups are performing compared to Audrey. You need to create a calculated field that gives you only Audrey's sales as denominator.
You can create that as follows
If [Product Name (group)] = 'Audrey'
then [Sales] else 0 end
Now you can create another calculated field that gives you the ratio of all users over Audrey
Sum([Sales]) / [Audrey Sales]
P.S : When you want percentages, don't multiply with 100, because tableau will understand and show the fractions as percentages by changing the format of the field. You can see how to do that here - Format Numbers and Null Values
Also may I know, why is this calculation necessary? I am asking this because your data might be in a way that is not easy to create the calculation you are looking for.
My client wants percentages displayed on the dashboard. From the mockup I was given they got to the figures by calculating it like how I presented it in the example screenshot. Thanks for your help