working with dynamic dropdown, and setting the final amount based on dropdown selection

Now it is 2017 , i hope that jotform might have find the solution of this problem.

in this image the lower dropdown will change according to previous dropdown.

and after selecting all the fields subtotal will be performed.

--My problem is that how to setup such dropdowns and how to set the price on these dropdown and prepare the subtotal.
----i know the basic calculation on jotform using the form calculator widget.

please help..