To calculate the number of shingles, we first calculate for the total area of the roof of Janice's house. From the figure, we can calculate the area of the two shapes: pyramid and a rectangular prism.
A(pyramid) = lw+l√[(w/2)²+h²]+w√[(l/2)²+h²]
A = 208 m²
A(prism) = 2(wl+hl+hw)
A = 293 m²
Total area = 501 m²
Number of shingles she needs = 501 m² / 2.25 m² = 223
