Let W = width of package
Let H = height of package
Let L = length of package
The perimeter cab be one of the following:
P = 2(L + W), or
P = 2(L + H)
The perimeter of the cross section cannot exceed 108 in.
When the width is 10 in, then
2(L + 10) <= 108
L + 10 <= 54
L <= 44 in
When the height is 15 in, then
2(L + 15) <= 108
L + 15 <= 54
L <= 39 in
To satisfy both of these conditions requires that L <= 39 in.
Answer: 39 inches
