7-разгеле=>100

function solve(arr) {
  let sums = [];

  /* arr.forEach(row => {
    let sum = row.reduce((a, b) => a + b, 0);
    sums.push(sum);
  }); */
  let lengthArr = arr.length
  let arrSum = 0

  for (let col = 0; col < lengthArr; col++) {
    for (let row = 0; row < lengthArr; row++)
      arrSum += arr[col][row]
    sums.push(arrSum)
    arrSum = 0
  }

  for (let i = 0; i < lengthArr; i++) {
    arrSum = 0;

    for (let j = 0; j < lengthArr; j++) {
      arrSum += arr[j][i];
    }

    sums.push(arrSum);
  }

  let equal = arr => arr.every(e => e === arr[0]);

  console.log(equal(sums));
}