Answer:
public static void display(int [] arr){
    System.out.print("Arrays: ");
        for(int i =0;i<arr.length;i++){
            System.out.print(arr[i]+" ");
        }
        System.out.println();
    }
    
public static void displayReverse (int [] arr){
    System.out.print("Arrays in reverse order: ");
        for(int i=arr.length-1;i>=0;i--){
            System.out.print(arr[i]+" ");
        }
        System.out.println();
    }
    
public static int displaySum (int [] arr){
    System.out.print("Sum: ");
    int sum = 0;
        for(int i =0;i<arr.length;i++){
            sum+=arr[i];
        }
        return sum;
    }
    
public static void displayLessThan (int [] arr, int num){
        System.out.print("Less than "+num+": ");
        for(int i =0;i<arr.length;i++){
            if(arr[i]<num){
                System.out.print(arr[i]+" ");
            }
        }
        System.out.println();
    }
public static void displayHigherThanAverage  (int [] arr){
        System.out.print("Higher than average: ");
        int sum = 0;
        for(int i =0;i<arr.length;i++){
            sum+=arr[i];
        }
        float average = sum/arr.length;
        for(int i =0;i<arr.length;i++){
            if(arr[i]>average){
                System.out.print(arr[i]+" ");
            }
        }
        System.out.println();
    }
Explanation:
<em>The methods were written in Java. See attachment for explanation where I used comments to explain each lines.</em>
<em>Note that lines that begin with double slash (//) are comments</em>