请问那里错啦，我没看出来

public class HelloWorld{

    public static void main(String[] args) {

           int age1=24;

            int age2=18;

            int age3=36;

            int age4=27;

            int sum=age1+age2+age3+age4;

            double avg=aum/4;

            int mainus=age1-age2;

            int newAge=--age1;

           System.out.println("年龄总和："+sum);

           System.out.println("平均年龄："+avg);

           System.out.println("年龄差值："+minus);

           System.out.println("自减后的年龄："+newAge);

}

}