The length of the second box is 76 inches.
If two shapes are similar in shapes, they tend to have corresponding sides, also be in a similar ratio and their corresponding angles are equal.
From the parameters given:
For the larger box, the area is = length × breadth
Area = 38 in× 6 in
Area = 228 inches²
For the smaller box;
Area = Length × width
Area = Length × 3 inches
Area = 3L inches
Using the relation of similar shapes:
228 inches² = 3L inches
Length (L) = 228 inches²/3
Length (L) = 76 inches
Learn more about similar shapes here:
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