Answer:
Part A answer: 0.5x + 3 = 18.50
How I got the answer: 0.5 means how much money she made from each cup. the variable x = how many she sold. 3 equals the tip from the neighbor. and 18.50 is the total price
Part B answer: (0.75x - 0.10x) + 3 = 21.00
How i got the answer: 0.75 is how much money she make from each cup. 0.10 means how many she paid for each cup she used. x = how many cups were sold/bought (should be the same number!). 3 is the tip. and 21.00 is the total price made.
Part C answer: The equations differ because Sydney didn't have to pay for the cups she used, while Daria did. Although they did have the same amount for a tip, Daria made more money than Sydney.
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this should be correct! hopes this help and i wish you good luck on your math exam!