68 boxes of a certain commodity require a shelf-length of 13.6 m. How many boxes of the same commodity would occupy a shelf length of 20.4 m?

Explanation

To solve the problem step by step, we will use the concept of direct variation. The number of boxes is directly proportional to the shelf length.

### Step-by-Step Solution:

1. **Identify the known values**:
- Number of boxes (B1) = 68
- Shelf length (L1) = 13.6 m
- Shelf length (L2) = 20.4 m
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