Add this code in an appropriate location for your product.
<div class="product"><input value="Bowl-A-Thon ticket Adult" class="product-title" type="hidden"><input value="60.00" class="product-price" type="hidden"><div title="Add to cart" role="button" tabindex="0" class="googlecart-add-button"></div></div>
<div class="product"><input value="Bowl-A-Thon ticket Child" class="product-title" type="hidden"><input value="20.00" class="product-price" type="hidden"><div title="Add to cart" role="button" tabindex="0" class="googlecart-add-button"></div></div>

Add this code only once for each html page, just before the </body> tag.
<script  id='googlecart-script' type='text/javascript' src='https://checkout.google.com/seller/gsc/v2_2/cart.js?mid=454818608780296' integration='jscart-wizard' post-cart-to-sandbox='false' currency='USD' productWeightUnits='LB'></script>