tmp.js

var time = 0;
var index = 15;
var index2 = 65.82;
var items = document.querySelectorAll('.js-duration strong')

for(var i=items.length;i--;){
  var value = items[i].innerHTML;
  var vals = value.split(':');
  var minutes = parseInt(vals[1]) * 60 + parseInt(vals[2])
  time += minutes;
}

var value = time / 60 * index;
var value2 = value * index2;

console.log(value, '|', value2);