You can split it to a triangle along with a rectangle underneath. Formula for calculating triangle: height x base divide by 2 Firstly we will have to calculate the triangle. 0.8x1.8/2 ( since 1.8 matches the base of the triangle we are looking for) which equals to =0.72 m Now let’s calculate the rectangle: 1.8 x 2.1 =3.78
Finally add them both together which is: 0.72+ 3.78= 4.5 m
