text: 
  function runningTotal(array) {
    return array.map((_, i) => array.slice(0, i+1).reduce((t, v) => t+ v));
  }
  
  
  
  
  
  
  console.log(runningTotal([2, 5, 13]));             // [2, 7, 20]
  console.log(runningTotal([14, 11, 7, 15, 20]));    // [14, 25, 32, 47, 67]
  console.log(runningTotal([3]));                    // [3]
  console.log(runningTotal([]));                     // []