How to add (sum up) values from multiple columns to a work item query?

I'm looking for a solution to add/substract/multiply/divide 2 columns of a work item query on the DevOps board.

Examples:

In my query result I want to see e.g.

- the remaining effort for a work item, automatically calculated from the columns OriginalEstimate(hrs) - EffortSpent(hrs) = RemainingEffort(hrs) or EffortSpent(hrs)/OriginalEstimate(hrs) = PercentDone

- the period between the StartedDate and the FinishedDate in days

On my dashboard I'd like to see e.g.

- a diagram displaying the average estimate/effort per issue type (issue type is a custom field value)

- a diagram displaying the average number of days (FinishedDate-StartedDate) per issue type (a custom field value) 

I couldn't find any out-of-the-box solution, no reasonably easy workaround and also no marketplace extension, so I appreciate your advice.