Explanation:
1) Total rectangle area = W x H = 12 x 8 = 96 cm^2
area of triangle (shaded portion) = 1/2 base * height = 1/2 * 7 x 8 = 28 cm^2
Nonshaded portion = 96 - 28 cm^2 = 68 cm^2
ratio shaded:nonshaded is then 28 : 68 = 7:17
2) Look at the two middle triangles : Height of each = 8 cm
then reading across the diagram height + base + height = 21 cm
so base = 5 cm
area of ONE triangle = 1/2 * base * height = 1/2 * 5 * 8 = 20 cm^2
total area for FOUR of them = 80 cm^2