function solve() {

   let addButtons = document.querySelectorAll('button.add-product');
   let checkoutBtn = document.querySelector('button.checkout');
   let outputElement = document.querySelector('textarea');
   let cart = {};

   addButtons.forEach(x => x.addEventListener('click' , function() {

      let addedProductName = x.parentNode.previousSibling.previousSibling.firstChild.nextSibling.textContent;
      let addedProductPrice = x.parentNode.nextSibling.nextSibling.textContent;

      if (!(cart.hasOwnProperty(addedProductName))) {

         cart[addedProductName] = 0;
      }
      cart[addedProductName] += +addedProductPrice;

      outputElement.value += `Added ${addedProductName} for ${addedProductPrice} to the cart.\n`;
   }));

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

      let totalPrice = Object.keys(cart).reduce((sum,key)=>sum+parseFloat(cart[key]||0),0);

      outputElement.value += `You bought ${Object.keys(cart).join(', ')} for ${totalPrice}.`;

      addButtons.forEach(x=>x.disabled = true);
      checkoutBtn.disabled = true;
   })
}