Answer:
The one that sells 10 tacos for $8.49
To get the better deal, you should find the selling prices for a single tacos in both cases and compare the amounts.
In the first one, 10 tacos for $8.49
This means 1 tacos sells for $8.49/10 = $0.849
In the second one, 6 for $5.40, this means for a single tacos, the selling price is $5.40/6 =$0.9
The better deal is the first one that sells one taco for $0.849 compared to the second one that sells one tacos for $0.9