A total of 30 coins, consisting of dimes and quarters, have a total value of $5.70. How many quarters are there?

✓ Correct Answer: Option B

Let d = dimes, q = quarters. d + q = 30 and 0.10d + 0.25q = 5.70. From d = 30 - q, substitute into the second equation: 0.10(30 - q) + 0.25q = 5.70. This simplifies to 3 + 0.15q = 5.70, so 0.15q = 2.70, and q = 18.