Answer:
Step-by-step explanation:
I'm not sure you will be satisfied with this but the area of a octagon is given by Area =2(1+√2)a²
Using this formula you get
a = 11 cm
Area = 2*(1 + √2)11²
Area = 2*(1 + 1.4142)*121
Area = 2*(2.4142)*121
Area = 4.8284*121
Area = 584.24
