select price by weight and classification

Question

I'm trying to set a "price" of a product by its classification and wight, for example, I have 3 types of classifications GOOD, OK, and BAD each classification has a price range according to its weight; for example, classification (GOOD < 100 = $price1, > 100 = $price2, ) , (ok < 100 = $price1, >100 = $price2, )and (bad <100 = $price1, >100 = $price2, ) if the product is classified as GOOD and the wight of the product is < 100 its $price1 is 25 , but if the product is classified as GOOD but wight > its $price2 is 20,

My database looks like this: table name classification each table has three columns: name, price1, price2, (price1 is for <100)(price2 is for >100)

this is what I have so far :

  product: <input   id="product"name="product">

  wight: <input  id="wight" name="wight>

  <label for="classifications"">classifications</label>


    <div class="selector-classifications">
   <select class="form-control" id="classifications" 
      name="classifications" required> 
  </select>
                                                </div>
                                            </div>


  price: <input  id="price" name="price">

the selector for classifications gets all the name of the classifications:

      $fetch = "SELECT * FROM classification "; 
  $result = mysqli_query($con, $fetch) or die("error");
  echo '<option value="0">choose option...</option>';
   while (($fila = mysqli_fetch_array($result)) != NULL) {
        echo '<option 
        value="'.$fila["name"].'">'.$fila["name"].'</option>';
        } 

my problem is that I'm trying to take the value of wight and classification to show its price in the price input without reloading the page, thanks in advance .