The lateral area of the pyramid is half the product of the perimeter and the slant height.
A = (1/2)Ph
A = (1/2)*(4*40 ft)*(18 ft) = 1440 ft²
This is 14.4×(100 ft²), so is 14.4 squares. Since 3 bundles are needed for each square of roof, Lourdes needs 14.4×3 = 43.2 bundles.
Lourdes should buy 44 bundles of shingles to cover the roof.
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43 bundles is not enough.