title: Swift sum numbers in array adding from specific element
body: <p>Let's say I have some numbers in an array like below</p>
  <pre><code>let numberArray = [1, 3, 4, 6, 9, 14, 16]
  </code></pre>
  <p>I know how to sum them all up by using reduce method but how can I start adding numbers from specific element. For example:</p>
  <pre><code>//Sum all up by reduce
  let sumAll = numberArray.reduce(0, +)
  //sumAll = 53 
  
  //I want to start counting from the fourth element in the array which is 6
  //so the total should be 45. [6 + 9 + 14 + 16]
  </code></pre>
  <p>What method should I use to achieve this?<br>
  Thanks in advance.</p>