I understood what you said. .what I don't understand is, why add 240 V? Isn't Vs= Is/Zline?

 

I understood what you said. .what I don't understand is, why add 240 V? Isn't Vs= Is/Zline?

No.
Firstly, voltage is current multiplied by impedance.
The load end of the line is 240V. The linevoltage drop must be added to this to give the total source voltage.

 

Thanks t_n_k

 

Ok! thank you. So, is Vs= 285 @ angle 1.94 ?

 

Ok! thank you. So, is Vs= 285 @ angle 1.94 ?

That's close enough - I have it as 286.3 @ +1.95 degrees [Volts]

Well done!