if(_in == '/n') {
Are you certain that slash is leaning the right way? I'm certain that it isn't.
_in = Serial.read;
Function calls require ().
Serial.read() returns a byte. Why are you storing that byte in a long?
number1 = Number.substring(0,6);
number2 = Number.substring(7);
The compiler is right. You can't do this. A substring can only be stored in a String.