Area of rectangle → 18 × 7.2 = 129.6 cm²

Area of ΔABE → ½ × 12 × 7.2 = 43.2 cm²

Area of ΔBCH → ½ × 6 × 7.2 = 21.6 cm²

129.6 – 43.2 – 21.6 = 64.8 cm²

Since BFGI is the intersection of the 2 triangles, it had been deducted twice. So we need to add its area back.

Area of shaded part → 64.8 + 21 = 85.8 cm²