If you want to allow your learners to use calculator while taking a mock test, you can easily do that from our quiz settings page.
Select the mock test for which you wanted to enable the calculator from Courses/Mock-tests dashboard
Once you are in the quiz builder page, you can see option called SETTINGS on Bottom-Left, click on the settings option
In the settings page, select Quiz features.
Scroll the page to see the option to enable or disabling the calculator. You can choose between Normal calculator and Scientific calculator from the drop down
Save the settings, and now you have successfully enabled calculator for that particular mock test