JSFiddle - React, Tailwind, and code Playground

HTML

<body></body>

JavaScript

var k;
 var i;
 var temp;

 //Declare an 8x8 matrix
 var MAT = new Array (8)
 for (i=0; i<8; i++) {
 MAT[i] = new Array (8);
 //Populate the matrix
 for (k=0; k<8;k++) {
 MAT[i][k] = Math.floor(Math.random() * 64); 
 }
 }

 //Create Array of length 22
 var grades = new Array (22);
 for (i=0; i<8; i++) {
 grades[i] = MAT[0][i]; //Top row of matrix into the array.
 grades[i+7] = MAT[6][i]; //Anti-diagonal row of matrix into the array.
 i=i+1;
 k=k-1;
 grades[i+14] = MAT[7][i] //Bottom row of matrix into the array.
 }

 //Sort the array

 for (i=0; I < 63; i= i++) {
 for (k=i+1; k<64; k++) {
 if (grades[i] > grades[k]) {
 temp = grades [k];
 grades[k] = grades [i];
 grades[i] = temp;
 }
 }
 }

 //Compute the average of the grades stored in the even locations of the array.

 var sum =0;
 var avg;

 for (i=0; i<100; i ++ 2) {
 sum=sum + grades [i];
 }

 avg = sum/50;
 document.write (avg);


 //Copy the array back into the matrix

 i=0;
 for (k=0; k<8; k++) {
 MAT[i][k] = grades[i];
 i = i+1;

 k=6
 for i=1; i <7; i++) {
 MAT[i][k] = grades [i];
 i=i+1;
 k=k-1;

 i=7
 for (k=1; k<8; k+1) {
 MAT[i][k] = grades [i];

 }
 }
 }

 //Display matrix

 document.write ( + MAT +);