There are a total of 12 sugar plum fairies.
Nine of the fairies will wear white tutus and the rest will wear pink tutus.
Six of the fairies have dark hair AND will wear white tutus.

Dakota wants to know how many of the fairies have light hair and will wear white tutus.

3

Step-by-step explanation:

Total Fairies = 12

Wear White Tutus = 9

So, Wear Pink Tutus = 12 - 9 = 3

Now,

6 have DARK HAIR & WHITE TUTUS, so that means out of 9 with white tutus, 6 of them have dark hair, so the rest would have light hair. How many is that:

9 - 6 = 3

So,

White Tutus = 9

White Tutus (Dark Hair) = 6

White Tutus (Light Hair) = 3

Dakota wants to know how many wear white tutus and have light hair. According to our discussion above, that will be 3 fairies.