To determine the new length in boxes when converting the scale from 1 box = 6 meters to 1 box = 3 meters, we first need to calculate the actual length that corresponds to the original scale.
1. The length of the rectangle in boxes is 7.
2. At the original scale (1 box = 6 meters), the actual length is:
\[
7 \text{ boxes} \times 6 \text{ meters/box} = 42 \text{ meters}
\]
Now, we need to convert this length into boxes using the new scale (1 box = 3 meters):
1. To find out how many boxes correspond to 42 meters at the new scale, we perform the following calculation:
\[
\frac{42 \text{ meters}}{3 \text{ meters/box}} = 14 \text{ boxes}
\]
Thus, the length in boxes of the new drawing will be **14**.