Answer: $17.50.
Step-by-step explanation;
If each muffin cost her $0.25 to make and she spent $8.75 making all muffins, then you can divide this amount to find out how many muffins she made (8.75/0.25), this is 35 muffins. If she sold each muffin for $0.50, multiply the number of muffins (35) by their price ($0.50), this is $17.50. Therefore, Maria received $17.50 from selling her muffins.