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Hi AtchayaP 

Ensure [Time created] and [Time closed] columns are both of Time data type, then you can create a new column with below DAX. This returns spent time in seconds for every row. 

Time in Second = DATEDIFF('Table'[Time created],'Table'[Time closed],SECOND)

Then create a measure to calculate the total of time spent. I format it to show result like "xx h xx m xx s".

Time Spent = 
VAR _totalSeconds = SUM('Table'[Time in Second])
VAR _hours = INT(_totalSeconds/3600)
VAR _minutes = INT(MOD(_totalSeconds,3600)/60)
VAR _seconds = MOD(MOD(_totalSeconds,3600),60)
RETURN
_hours&"h"&_minutes&"m"&_seconds&"s"

If you drag [Time in Second] column into a card visual directly and select SUM aggregation type for it, it will show the total time spent in seconds. It equals to above result. 

Best Regards,
Community Support Team _ Jing
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