You need to create a new column in the custom Order table. The Dataverse table contains information about every order. The new column should store the number of days since the order record was created for the open (new) orders. The column should update the value whenever you save the record. 
What should be the type of the new column?

Answer options:

A.Whole number
B.Rollup
C.Decimal number
D.Calculation
E.Duration

Correct Answer: D 
Microsoft Dataverse provides special column types for calculations and data aggregation. These types are Calculation and Rollup. 
The Calculation column allows users to define a formula based on the column value. This type includes columns from the same table and related parent table in a many-to-one relationship. Calculated columns are read-only. Users benefit from a list of built-in functions for the calculated values. This column type operates on the different data types like text, numeric, and date-time. The calculations run synchronously when a record is saved. 
The Rollup column is like the Calculated type. The Rollup type operates only on the numeric (Whole Number, Decimal Number, and Currency) and date-time datatypes. This type includes columns from the same table and related child tables in a one-to-many relationship. The list of built-in functions for the Rollup column is smaller compared to the Calculated columns. It includes sum, min, max, and count. Rollup columns are read-only. By default, the calculations for the Rollup column run once per hour. Users can change the frequency in Customization settings for the table. It is an asynchronous operation. 
Suppose you create the calculated column “DaysOpen.” Here is the condition and action for the column: 

The condition includes the check for the “New” order status. And the action has the Difference in days between the order date and a current date/time. If you use the NOW() function, you need to be sure that the date-time column’s behavior is set to the “User local” (in this case, the nwind_orderdate or “Order date” column (Number 1)). The “User local” behavior (Number 2) stores the time zone-aware data. This type of date-time behavior is the requirement for the NOW() operations. 

Options A, B, and D are incorrect because the Duration, Whole number, and Decimal number are the data types but not the column types.
For more information about The Dataverse Calculated and Rollup columns, please visit the below URLs: 

https://docs.microsoft.com/en-us/learn/modules/create-define-calculation-rollup-fields/3-calculation
https://docs.microsoft.com/en-us/learn/modules/create-define-calculation-rollup-fields/3-calculation
https://docs.microsoft.com/en-us/powerapps/developer/data-platform/calculated-rollup-attributes