The dropdown list doesn't display the other dropdown values

Please I'm new with JavaScript and I need your help with this :

I've created 7 dropdown lists: "Product", "StoreA", "StoreB", "StoreC", "StoreD", "StoreE" and "DeliveryTime".

Each dropdown list has the following values :

- "Product" : "Select an item", "Item 1", "Item 2", "Item 3" and "Item 4"

- "StoreA" : " "

- "StoreB" : "Store 1"

- "StoreC" : "Store 2"

- "StoreD" : "Store 3", "Store 4"

- "StoreE" : "Store 5"

The  "StoreA", "StoreB", "StoreC", "StoreD", and "StoreE" are visible/hide based on a value from the "Product" dropdown list. I made a javascript code adequate in a custom validation script and it works pefectly!

My issue is with the "DeliveryTime", I want it to be populated based on the dropdown list visiblity  :

- if "StoreA" is visible then "DeliveryTime" = " "

- if "StoreB" is visible then "DeliveryTime" = "5 days"

- if "StoreC" is visible then "DeliveryTime" = "6 days"

- if "StoreD" is visible : with the value "Store 3" the "DeliveryTime" = "3 days or 7 days", and with the value "Store 4" the "DeliveryTime" =  "4 days"

- if "StoreE" is visible then "DeliveryTime" = "3 days or 7 days"

but the code that I made for this doesn't work. the file is in the attachment and sorry to be so long-winded