Shopify Plus + Free Shipping issue (using Script Editor, must be fluent in Ruby)

***Only respond if you can take this on immediately please.*** Should take less than 1 or 2 hours. Need to use Script Editor to make the Free shipping for U.S. orders over $50 apply to the final cart amount, not the amount before a discount is applied. We're running a Black Friday sale right now and, as an example, if the initial cart value is $60 and they apply a 30% discount ($18.00) with the code so that their order total is now $42.00, they are still getting served the free shipping option. We need to make it so the Free shipping option only shows when their total order volume is $50 or more after any discounts are applied. We currently have 17 active coupons on the site that this will need to take into account.