as you see, each two triangles beside each other are identical, so I will find one from each two and then add all together.
Area of triangle 1 (largest) = base x height / 2
= 7 x 9 / 2
= 63 / 2
= 31.5
Two of them = 31.5 x 2 = 63
Area of triangle 2 (smallest) = 4 x 7 / 2
= 28 / 2
= 14
Two of them = 14 x 2 = 28
Total = 28 + 63
= 91 cm^2
