How to calculate the composite's elements and get total of them?

Hi I have a composite that has a QTY field and a TOTAL PRICE field and the table below would calculate and display the subtotal. It works properly when there is only one row of composite, but when I add more items, the subtotal field displays two subtotals instead of one as a whole. I want the subtotal field to display 24 instead of 4 and 20. How can twig solve this implementation? In my SUBTOTAL, I have

    {% for item in data.item %} 
    {% set total_qty = (item.qty)|number_format(2,'.',',') %} 
    {% set per_price = (item.total)|number_format(2,'.',',') %} 
    {% set net_cost = (total_qty * per_price )|number_format(2,'.',',') %} 
    {{ net_cost }} 
    {% endfor %}

Here is the screenshot to give you better understanding

Don't output the net cost inside the for loop. First create the sum, then display it after the loop.
Also don't use number_format before the final result.

{% set net_cost = 0 %}
{% for item in data.items %}
    {% set net_cost = nest_cost + item.qty * item.total %}
{% endfor %}

{{ net_cost|number_format(2, '.', ',') }}

demo