I have created a formula for calculating the difference of

Question

I have created a formula for the difference of two times , it works fine and returning all rows 

 

now i want the sum of all these rows which return the difference of two dates for that i have applied that formula

 

NumberVar TotalSec := Time({zz_tbl_Report_New_Format.MondayOut}) - Time({zz_tbl_Report_New_Format.MondayIn});

NumberVar Hours := Truncate ( TotalSec / 3600);

NumberVar Minutes := Truncate (Remainder ( TotalSec,3600) / 60);

Totext ( Hours, '####') + ':'+ Totext ( Minutes,'00');

 

Now I want to calculate the sume how can i achieve that