Please share your formula. A 10 day duration task starting on a Monday and ending 10 working days later is really only 12 calendar days (assuming Saturday and Sunday are non-working) - so I don't know how you got 14 days.

What date/time does the task begin and end?

Regarding your second question:
Question 2) This one I did as experiment. I did not used “work” column in this schedule before so everything was zero. I inserted a work column, and for this task I assigned a random work amount of 100
But when I did the changes as stated above, the 100 never changed, for any option. Why?

Work is not related to duration unless you have resources assigned to the task. It is the assignment units (Peak) that creates the relationship between work and duration. Assuming the task is fixed units and you have resource(s) assigned - if you increase duration, work will increase. But without assignments, there is no relationship between work and duration.

Regarding:
Question 3) something is fixed for this task and when I change my calendars it is just dividing that fixed quantity to find the new calendar day duration. If it is fixed units, I don’t see a column for it. How can I see that fixed thing that the calculations are based upon? Also when I change to 24 hour calendar, would it not be 3.33 days? Why is it 3?

i don't understand "something is fixed for this task". Are you referring to task type (Fixed Duration, Fixed Units, Fixed Work)? These have no impact unless you have resource assigned. The definition of a day is 8 hours - if you change to a 24 hours calendar the "day" definition doesn't change. Depending upon when the task begins and ends, you may see 3.33 days or 3 days.
Please post your formula.