The form is not adding the amounts of each selection to the total

The sharks fish and chicken form will not add selections into a sub total and total, it seems like it is only taking one item at a time into the amount box. I need for customers to be able to select their items, and the form to calculate all items and pay.

I also need to add a box for a delivery fee which will never change.

I also need to add a quantity box for each item.

Could you please tell me how to do these three things. Thanks 

I see that you can set calculation values in your items. However, the form calculation widget does not add or sum up items because you did not add (+) additions, see screenshot below.

I also need to add a box for a delivery fee which will never change.

Add a short text entry field or form calculation widget and then assign default values. You can then add this in your form calculation widget.

I also need to add a quantity box for each item.

If you want to add a quantity box for each item then you need to separate all of your items to one checkbox field per item and then add dropdown or textbox for quantity. After that, add calculation widget that will multiply the value of the item and quantity (you can set this hidden).

Guide: How-to-Perform-Form-Calculation-Using-a-Widget