The tires Mary wants to buy for her car cost $200 per tire. A store is offering the following deal. Buy a tire and get the 4th tire for 75% off!

Mary will buy 4 tires using the deal. A sales tax of 8% will be charged after applying the discount. How much money will Mary saveby using the deal instead of paying the full price for all 4 tires?
(With deal and without deal)

Carla was trying to decide what to do saturday evening. she has $100 available to spend for the evening. she has narrowed her choices down to these events: braves game, a concert of an artist she likes, or the georgia aquarium. admission to the braves game is $25, hot dogs cost $10, sodas cost $5. the concert costs $25 for admission, $20 for a souvernir t-shirt, and $10 for a soda. the georgia aquarium has the show of a lifetime with an all you can eat and drink that costs $100. carla does not want to take any driving chances, so in addition to the cost of the aquarium, she will also need to pay for her uber/lyft, which is $15 each way. which option should carla choose if she wants to spend the least? based on that choice, what then is carla's oppotunity cost? fully explain your answer in at least one paragraph.