Track users login and logout time and calculate working hours in ASP.Net

how to calculate the hours

like mrg 10 to 5 total 7 hrs

if i login in 10.30 and logout at 5.30 same 7 hrs me wrokked

now i logi at 10.15 and logout at 5.30 7.45 7hrs and 45 mins me worked i need to calculate the min and hrs