We can divide the pentagon into a rectangle (on the left) and a triangle (on the right)
The dimensions of the rectangle are 8x10 cm, so its area is
[tex]8\cdot 10=80\text{ cm}^2[/tex]
The triangle has the same base as the rectangle, and its height is the difference between the sides of 15 and 10: the area is
[tex]\dfrac{8\cdot (15-10)}{2} = 4\cdot 5 = 20\text{ cm}^2[/tex]
So, the total area is
[tex]80\text{ cm}^2+20\text{ cm}^2=100\text{ cm}^2[/tex]
