How do you insert a function that will calculate the average retail price of the available toppings?

To insert a function that calculates the average retail price of available toppings, you would first need to collect the prices of the toppings into a list or array. Then, you can create a function that sums these prices and divides the total by the number of toppings. In Python, for example, the function could look like this:

<code class="language-python">def average_price(prices):
return sum(prices) / len(prices) if prices else 0
</code>

You would call this function by passing the list of topping prices as an argument.