public static void main ( String [ ] args ) {
  Scanner scanner = new Scanner ( System . in ) ;
  int t = scanner . nextInt ( ) ;
  for ( int i = 0 ;
  i < t ;
  i ++ ) {
    long a = scanner . nextLong ( ) , res = 0 , b = scanner . nextLong ( ) , k = scanner . nextLong ( ) ;
    if ( k % 2 == 0 ) {
      res += k / 2 * ( a - b ) ;
    }
    else {
      res += ( k + 1 ) / 2 * a - k / 2 * b ;
    }
    System . out . println ( res ) ;
  }
}

public static void main ( String [ ] args ) { Scanner scanner = new Scanner ( System . in ) ; int t = scanner . nextInt ( ) ; for ( int i = 0 ; i < t ; i ++ ) { long a = scanner . nextLong ( ) , res = 0 , b = scanner . nextLong ( ) , k = scanner . nextLong ( ) ; if ( k % 2 == 0 ) { res += k / 2 * ( a - b ) ; } else { res += ( k + 1 ) / 2 * a - k / 2 * b ; } System . out . println ( res ) ; } }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (array_type element: (type_identifier) dimensions: (dimensions)) name: (identifier))) body: (block (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (type_identifier) arguments: (argument_list (field_access object: (identifier) field: (identifier)))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) condition: (binary_expression left: (identifier) right: (identifier)) update: (update_expression (identifier)) body: (block (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal)) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))))))) alternative: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (binary_expression left: (binary_expression left: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (decimal_integer_literal)) right: (identifier)) right: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (identifier))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))))))