If 3/8 of the combined wheat and white flour is wheat flour, then the remaining 5/8 must be white flour. Let's calculate the amount of white flour needed:
Total flour = 3 cups
Wheat flour = (3/8) * Total flour = (3/8) * 3 cups = 9/8 cups
Since the total flour is a combination of wheat and white flour, the amount of white flour is given by:
White flour = Total flour - Wheat flour = 3 cups - (9/8) cups
To compute the subtraction, we need a common denominator:
White flour = 24/8 - 9/8 = 15/8 cups
Therefore, you would need 15/8 cups (or 1 7/8 cups) of white flour for the recipe.