Subtraction Quiz Program

[Schonge]

Having a problem with my Subtraction Quiz program on a specific line!

output += "\n" + number1 "-" + number2 + "=" + answer + ((number1 - number2 == answer) ? " correct" : " wrong") ;

The rest of the program seems to work except that output. It gives an error of " ';' expected "
Code Here:

public static void main(String[] args)
    {
        final int NUMBER_OF_QUESTIONS = 10 ;
        int correctCount = 0 ;
        int count = 0 ;
        long startTime = System.currentTimeMillis() ;
        String output = "" ;
        Scanner input = new Scanner(System.in) ;
        
        while(count < NUMBER_OF_QUESTIONS) {
            int number1 = (int)(Math.random() * 15) ;
            int number2 = (int)(Math.random() * 15) ;
            
            if(number1 < number2) {
                int temp = number1 ;
                number1 = number2 ;
                number2 = temp ;
            }
            
            System.out.print("What is " + number1 + " - " + number2 + "?") ;
            int answer = input.nextInt() ;
            
            if(number1 - number2 == answer) {
                System.out.println("You are correct!") ;
                correctCount++ ;
            } else {
                System.out.println("Your answer is wrong. \n" + number1 + " - " + number2 + " should be " + (number1 - number2)) ;
                count++ ;
            
                output += "\n" + number1 "-" + number2 + "=" + answer + ((number1 - number2 == answer) ? " correct" : " wrong") ;
            }
            long endTime = System.currentTimeMillis() ;
            long testTime = endTime - startTime ;
            
            System.out.println("Current count is " + correctCount + "\nTest time is " + testTime / 1000 + " seconds\n" + output) ;
        }
    }