Notice that area of triangle BIE = 1/2 * width (IE) * height (22cm)
also, area of triangle CIJ = 1/2 * width (IJ) * height (22cm)
the two triangles overlap on the quadrilateral FGHI.
so sum of triangles – FGHI = unshaded area.
we don’t know IE and IJ but we know that IE plus IJ = 50cm and since we’re adding the areas of the triangles,
BIE + CIJ = 1/2 * IE * 22 + 1/2 * IJ * 22
= 1/2 * 22 * (IE + IJ)
= 1/2 * 22 * 50
= 550cm2
unshaded area = 550 – 100 = 450cm2
shaded area = 50*22 – 450 = 650cm2