3/5 I think is the answer
<span>Euclid is considered the father of Geometry.</span>
12 ft * 10 ft = 120 sq ft
½ * 6 ft * 7 ft = 21 sq ft
120 sq ft - 21 sq ft = 99 sq ft (it is area of the composite shape)
we know that
the volume of a rectangular prism is equal to

where
L is the length of the box
W is the width of the box
H is is the height of the box
in this problem we have




<u>Find the length of the box</u>
Using a graph tool-------> we will determine the roots of the equation of volume
see the attached figure
the roots are

so

therefore
<u>the answer is</u>
the length of the box is equal to 
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