yes.But you have to cast that variable before adding.

eg:
byte b=(byte)b1+(byte)b2

yes, but u require type casting because the the binary
operation in java should atleast returns Integer values


example : 
    byte a=12;
    byte b=23;
//  byte c=a+b; //Not OK,bcoz a+b is an int value
    int c=(byte)a+b;   // OK

Yes,the following is the right way to do so
byte b1=21;byte b2=11;
	 byte b;
	 b=(byte)(b1+b2);