How to clear a field when an option is unchecked?

Also can I make the form clear the amounted enetred into a box if the main tick box above is unticked?

I understand that you want to clear the amount in the 'Sub Total' field when the field 'Setup fee' field is unchecked. As mentioned in my earlier response on the other thread https://www.jotform.com/answers/1268036/, using the multiple choice field should allow the user unchecking the option. Since the calculation value is already set on the field, when the option is unchecked the amount should be cleared in the 'Sub total' field.

Hope this information helps! 

Thanks, but I'm also referring to if someone selected large candles x 10 and also melts x 10 and then decided they didn't want the candles anymore and unticked candles option at the top, this doesn't clear the amount entered for the candles- so people could easily get confused or over charged. 

Thanks for the additional details. 

I can see what you're referring to and it seems to be fixed by clearing up the values for hidden fields, this can be done by going to the settings tab, form settings section and clicking on the show more button: 

Scroll a bit down and select the "Clear on being hidden" option on the "Clear hidden fields" drop down: 

You can see the result on this cloned form of yours: https://form.jotform.com/72816640876971 

I hope this helps.