Calculating Working Hours calculate from Time Colums

[Allen01]

Hi, I'm new in power bi

I'm trying to calcualate engineer total working hours from End Time - Start Time.

When I use in query in Excel I can use End Time - Strat Time with substract (Duration). When I present chart format I just need to add Total Working Hrs Cloums to Value field and my sum time is display. 

But when I use in power bi duration data is not show as [hh]:mm format. 

I would like to get idea 

1) Duration to [hh]:mm Format (That can sum in value field)

2) End Time - Start Time = Time Format ( That can sum in value field) 

I would like to show as below chart table (Total support Ticket Number & Total working Hours) 

query chart 

I already try from below link but not yet work for me. Please kindly help me for some solution. 

https://www.mssqltips.com/sqlservertip/7061/calculate-date-difference-power-bi-dax-datediff/

https://powerusers.microsoft.com/t5/Power-Query/Converting-Decimal-Hour-to-HH-MM-Format/m-p/1377637#...

https://community.powerbi.com/t5/Quick-Measures-Gallery/Net-Work-Days/m-p/367362#M109 (use dayhoursminute) 

[Allen01]

@Anonymous 

Thank you for your solution. But when I try 

(1) Total working hour = format([end time] - [start time],"hh:mm:ss")

it's show the time that I want but when i use this column in the report values field it's count not show as sum. 

When i add new column and use this formula 

(2) sum of time = FORMAT(SUMX(Allen,Allen[End Time] - Allen[Start Time]),"HH:MM:SS")

it's show diffrent time then actual working hours. 

Maybe I'm doing wrong. Can you explain to me in the power bi i need to use new column for (1) and (2) or (2) is measure of cloumn (1) ? 

Thank you for your help. 

[Anonymous]

Hello could you please try 

Total working hour = format([end time] - [start time],"hh:mm:ss")

 and to find the sum use:

sum of time = FORMAT(SUMX(Allen,Allen[End Time] - Allen[Start Time]),"HH:MM:SS")