Average auto calculation

Hi, here in my document (created with indesign) I have 3 dropdown menu (1 to 10)

and i would like the average to be automatically calculated. Can it shows on the line above (the one with the danger leveled from 1 to 10?

or in another field?

when i try to do it, I create a new field, put an average in it but I can not select my 3 dropdowns...it doesnt click..

Ideally, i would have the average showing in the line from one to ten to show the risk level...is it doable?

hope someone can help me!!

thanks!!