Multiply Export Values of DropDown boxes

I have a project - a fillable PDF form - I'm working on that requires me to multiply the export values from two dropdown lists

Dropdown1 has 4 entries, each with its own Export Value

Dropdown2 has 3 entries, each with its own Export Value.

So if a user selects the third option from Dropdown1 and the second option from Dropdown2, I'd like to multiply those two Export Values and pop the answer into a text field.

For example, I select option 4 on Dropdown 1 (Export Value of 380) and option 2 on Dropdown2 (Export Value of 3) - so the answer in the text field would then be 1140.

I'm aware of the Calculation Tab in the Properties window of the text field in which I'd like the final answer to be, and I'm aware I'd need to use a script to accomplish this, but I'm very green when it comes to Javascript. I can do basics, like populate a text field with a selected value from one of the Dropdown boxes. But I can't figure out how to multiply the two selected values.

Any help would be greatly appreciated.