Let's calculate the total cost of the Granny Smith apples first.
Dahlia bought 6 Granny Smith apples at $1.35 each.
Cost of Granny Smith apples = \( 6 \times 1.35 = 8.10 \)
Now, we know the total cost for both types of apples is $15. Therefore, we can find the total cost for the Macintosh apples:
Total cost for Macintosh apples = Total cost - Cost of Granny Smith apples
Total cost for Macintosh apples = \( 15 - 8.10 = 6.90 \)
Dahlia also bought 6 Macintosh apples. To find the cost of each Macintosh apple, we divide the total cost of the Macintosh apples by the number of Macintosh apples:
Cost of each Macintosh apple = \( \frac{6.90}{6} = 1.15 \)
Thus, the cost of each Macintosh apple is $1.15.