I want to addition of last duriation and current duration of timer

Hi, everybody, I am new comer, I am working of project, in that i have configure event counter and timer, in short i am going to count event i.e. on my 16 x 2 LCD shows IN:1, OUT:1, IN:02.35sec, TN:00.00sec, here at first when someone entered in room then IN:1, if he is out then LCD Shows OUT:1 and another IN:02.35sec, shows time spend, if again someone entered in the room then first IN:2 , then if he has came out from room, OUT: 2, and Another IN IN:05.35sec, Now i want to Count total Time spends (Means 1st time plus 2nd time = TN(Total time spend in roomentered_cameout_object_lcd.ino (2.2 KB)

Hello and good morning
And the question is?

I want to addition of previous time spend and current time spendentered_cameout_object_lcd.ino (2.2 KB)

In LCD in 1st column IN= No. of entered in room, below OUT= came out from room, then in 2nd column IN: Time spends , then TN=below total Addition of time spends (Means previous time spends plus (Add) current time spend , SO i am confusing in Total time spends, please help me