var subBtn = document.getElementById('submit');

​

subBtn.addEventListener('click', function() {

  highestSum();

  mostExpensive();

});

​

function mostExpensive() {

  var values = [];

  var cells = document.querySelectorAll('.my-table tbody td');

  for (var i=0; i<cells.length; ++i) {

    var cell = cells[i];

    var input = cell.querySelector('input');

    values.push(Number(input.value));

  }

  var max = Math.max.apply(Math, values);

  var key = values.indexOf(max);

  addClass(cells[key].parentNode, 'most-expensive');

}

​

function highestSum() {

  var rows = document.querySelectorAll('.my-table tbody tr');

  var sums = [];

  for (var i=0; i<rows.length; ++i) {

    var row = rows[i];

    sums.push(sumRow(row));

  }

  var max = Math.max.apply(Math, sums);

  var key = sums.indexOf(max);

  addClass(rows[key], 'highest-sum');

}

​

function sumRow(row) {

  var sum = 0;

  var inputs = row.querySelectorAll('input');

  for (var i=0; i<inputs.length; ++i) {

    sum+= Number(inputs[i].value);

  }

  return sum;

}

​

function addClass(elem, cls) {

  var current = elem.className;

  cls = (current) ? ' '+cls : cls;

  elem.className+= cls;

}