title: Sum of value in a collection using flutter
body: <p>I have a list/collection and I need to get the sum of all prices in this list.</p>
  
  <pre class="lang-dart prettyprint-override"><code>cart_items = [
      {
          "id": 144,
          "created_at": "2019-04-04 14:42:04",
          "updated_at": "2019-04-04 14:42:04",
          "cart_id": "3",
          "client_id": "83",
          "product_id": "6",
          "quantity": "1",
          "price": "1500",
          "name": "Cucumber (2Pcs)",
          "image": "products/es4eGjkgQ6MvzTaMyX4iXWjcSX03mVk3QB9oODWk.jpeg",
         },
      {
          "id": 145,
          "created_at": "2019-04-04 14:42:09",
          "updated_at": "2019-04-04 14:42:09",
          "cart_id": "3",
          "client_id": "83",
          "product_id": "5",
          "quantity": "1",
          "price": "2000",
          "name": "Cauliflower",
          "image": "products/lVZ31zORzltyVIDXhHoCWUgjTlal7cWd7pI8DL2V.jpeg",
          }
  ]
  </code></pre>
  
  <p>I have been trying to use the reduce method on this collection/list but I don't know how to specify that I need to get the sum for price.</p>