Explanation:
ED || AB
E is the midpoint of AC.
therefore, D is the midpoint of BC, and AB is 2×ED.
but also the height of ABC is 2×height of EDC.
now, we know, the area of a triangle is
baseline × height / 2
area EDC = baseline × height / 2 = 18 cm²
area ABC = 2×baseline × 2×height /2 =
= 4 × (baseline × height / 2) =
= 4 × area EDC = 4 × 18 = 72 cm²
the area of ABDE = area ABC - area EDC =
= 72 - 18 = 54 cm²