We have to determine the best cost after all discounts and tax.
Hamburger:
1 pound of Open Acres = $2.39
30 pounds of Open Acres = 
10% off is provided if we buy at least 10 pounds of Open Acres, we bought 30 pounds. So, we get 10% off.
10% off on 30 pounds of Open Acres Hamburgers = 10% of $71.7
= 
Total cost of 30 pounds of Open Acres Hamburgers = $71.7 - $7.17
=$64.53
Buns:
1 packet of Burly buns = $1.93
15 packets of Burly buns = 
=$28.95
5% off on 15 packets of Burly buns = 5% of $28.95
= 
Total cost of 15 packets of Burly buns = $28.95 - $1.4475
=$27.50
Now, according to the question, a 10%-off coupon that can be used on either the hamburger or the buns, but not both, after any other discounts are applied.
Let us apply 10% off applied on Hamburgers:
10% of $64.53
=
Now, total cost of hamburgers after all the discounts = $64.53-$6.453
= $58.077
And total cost of Buns after all the discounts = $27.50
Total price of hamburgers and buns = $58.077 + $27.50
= $85.577
5% tax applied on total price of hamburgers and buns = 5% of $85.577
= $4.28
Best cost on the purchase of hamburgers and buns = $85.577 + $4.28
= $89.857
Rounding to the nearest hundredth dollar, we get
Best cost on purchase of 30 pounds of hamburgers and 15 packets of buns after all discounts and tax = $89.86
