public static void main ( String [ ] args ) {
  Scanner scan = new Scanner ( System . in ) ;
  int cases = scan . nextInt ( ) ;
  long a , b , k ;
  long x = 0 ;
  ArrayList < Long > results = new ArrayList ( ) ;
  for ( int i = 0 ;
  i < cases ;
  i ++ ) {
    a = scan . nextLong ( ) ;
    b = scan . nextLong ( ) ;
    k = scan . nextLong ( ) ;
    if ( k % 2 == 0 ) x = ( a * ( k / 2 ) - b * ( k / 2 ) ) ;
    elsex = ( a * ( k / 2 + 1 ) - b * ( k / 2 ) ) ;
    results . add ( x ) ;
    x = 0 ;
  }
  for ( int i = 0 ;
  i < results . size ( ) ;
  i ++ ) System . out . println ( results . get ( i ) ) ;
}

public static void main ( String [ ] args ) { Scanner scan = new Scanner ( System . in ) ; int cases = scan . nextInt ( ) ; long a , b , k ; long x = 0 ; ArrayList < Long > results = new ArrayList ( ) ; for ( int i = 0 ; i < cases ; i ++ ) { a = scan . nextLong ( ) ; b = scan . nextLong ( ) ; k = scan . nextLong ( ) ; if ( k % 2 == 0 ) x = ( a * ( k / 2 ) - b * ( k / 2 ) ) ; elsex = ( a * ( k / 2 + 1 ) - b * ( k / 2 ) ) ; results . add ( x ) ; x = 0 ; } for ( int i = 0 ; i < results . size ( ) ; i ++ ) System . out . println ( results . get ( i ) ) ; }
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