Calculate value from 3 rows only and add as extra row in table or matrix visual

[Evanooruvan]

I have this matrix visual in powerbi

Now i want to add a extra row in matrix visual combining bxx,exx,fxx ( named as BEF) 
How to calculate values like below visual in powerbi matrix,

[amitchandak]

@Evanooruvan , Have one dimension with an additional row, 

check these two solutions where i added an additional row with custom calculation

Show Grand total row or Avg Grand total row in Visual: https://youtu.be/OSwRZ4GUhxc

Power BI Modeling- Unselected values as others - https://youtu.be/HX4pgexYwf4

the idea is have additional calc using this method