Need help setting up a tax exempt button on a calculable form

[danieldmyers]

This is for a towing company form I'm creating, and I'm stumped by the JavaScript I need to setup in order to calculate the grand total based on whether or not an account is taxed or tax exempt. The existing fields are as follows:

(1) Total Trip Miles ["MILES"]  x  (2) Dollars/Mile ["RATE"]  =  (4) Total Mileage Fees ["MILEAGE"] +  (3) Tow/Hook Fee ("HOOK")  +  (5) "PAYOUT" [*This figure is NEVER taxed*]  +  (6) "OTHER" Fees  =  (7) "SUBTOTAL"  +  (8) "TAX" (@7.5%)  -  (9) "DISCOUNT"  =  (10) Grand Total "TOTAL"

The following fields are currently calculated using these commands:

- (4) MILEAGE: Value is the {Product} of "MILES, RATE"

- (7) SUBTOTAL: Value is the {Sum} of "HOOK, MILEAGE, PAYOUT, OTHER"

- (8) TAX: [Simplified Field Notation] "(HOOK+MILEAGE+OTHER)*0.075"

- (10) GRAND TOTAL: [Simplified Field Notation] "(SUBTOTAL+TAX)-DISCOUNT"

What I need is a 'Tax Exempt?' checkbox adjacent to the existing tax field that, when selected, will calculate the grand total based on the subtotal minus any discounts, but without tax. I realize there is probably some easier way to have conveyed what I need, but I am entirely befuzzled by custom calculations, so please bear with me and try to explain what I need to do in laymen's terms... thank you so much for anyone willing to help!

[Nesa Nurani]

I added checkbox and code to your file see if thats what you wanted

https://drive.google.com/uc?export=download&id=1ihQcJ_6yYm0BryeP88NFgsiFKOKu8Q1n 

Code is in TOTAL field.

[danieldmyers]

Wow - thank you so much! Is there any way to zero-out the tax dollar amount when the 'exemption' box is checked? We really have to spell things out for some of our drivers, and I don't want there to be any confusion as to whether or not the total is taxed -- lol.

[Nesa Nurani · Accepted solution]

Sure, try now.

https://drive.google.com/uc?export=download&id=1HCIfeTrplitGsJq5mASrLfTpC9pW_yTi 

[danieldmyers]

You are a lifesaver! Thank you for saving me a ton of headache.