Answer:
6 brownies and 2 cupcakes.
Explanation:
Let the number of brownies be b and the number of cupckes be c.
We have the following system:
b = 3c
1.5b + 3c = 15
Substituting for b in the second equation:
4.5c + 3c = 15
7.5c = 15
c = 2.
Thus b = 3c = 6.