Answer: Laura sold 32 boxes , Kelly sold 17 boxes and Tia sold 34 boxes.
Explanation:
Let the number of boxes bought by Laura be x.
Then, the number of boxes bought by Kelly be x-15
and the number of boxes bought by Tia = 2(x-15)
According to the question , we have

Then,

Hence, Laura sold 32 boxes , Kelly sold 17 boxes and Tia sold 34 boxes.