Need Quoting form plugin

I don’t know how to code PHP, but I need a small form which works like this:
1. the user chooses an option from the drop down menu (the option is assigned a number e.g. 8)
2. then enters the quantity of the option chosen (e.g. 20)
3. the form multiplies 20 by 8 and gives 160 below the small form.

I need to display it in my page or post.

Is there a plugin available to do this? or is there one available which can be modified to do so?

thank you