To solve this problem, we need to find out how many cups of flour are needed for 30 muffins, based on the ratio provided in the recipe.

1. Determine how much flour is needed for 1 muffin:

   The recipe uses 2.5 cups of flour for 12 muffins. To find the flour required for 1 muffin:

   $\text{Flour per muffin} = \frac{2.5 \, \text{cups}}{12 \, \text{muffins}} = \frac{2.5}{12} = 0.2083 \, \text{cups per muffin}$

2. Determine how much flour is needed for 30 muffins:

   Now, to find the flour needed for 30 muffins, multiply the amount of flour per muffin by 30:

   $\text{Flour for 30 muffins} = 0.2083 \, \text{cups} \times 30 = 6.25 \, \text{cups}$

So, 6.25 cups of flour are needed to make 30 muffins.

The correct answer is B. 6.25 cups.

Would you like further explanation on the method, or do you have any other questions? Here are some related questions you might find interesting:

1. How do you adjust a recipe if the number of servings is doubled or halved?
2. What are some other methods to scale recipes for different serving sizes?
3. How can proportions be used in everyday scenarios like cooking or mixing materials?
4. How do you convert between different units of volume (e.g., cups to liters)?
5. Can you calculate the amount of sugar or other ingredients using the same method?

Tip: When adjusting recipes, make sure you scale all ingredients proportionally, not just the main ingredients like flour!