First symmetrically cut the pentagon to get 5 pieces. (So that you will get the idea that this polygon is divided into 5 triangles)
Then find the area of one of the triangles:
Area of Triangle =
A =
× 4 × 10
A = 20 m²
To find the area of the whole pentagon shape:
A = 20 × 5 = 100 m²
Hope it helps!