Answer:
The number of small boxes is 9 and the number of large boxes is 3
Step-by-step explanation:
Let x be the number of large boxes.
The camp bought 3 times as many small boxes as large boxes, then the number of small boxes is 3x.
Each small box has 6 granola bars, then there are granola bars in 3x small boxes.
Each large box has 12 granola bars, then there are granola bars in x large boxes.
All boxes had 90 granola bars, so