Answer:
27 square units
Explanation:
To use Heron's formula, you need to know that "s" represents half the perimeter.
s = (11 +6 +9)/2 = 13
Then the area is given by the formula as ...
A = √(13(13 -11)(13 -6)(13 -9)) = √(13·2·7·4) = √728
A ≈ 26.98 ≈ 27 . . . square units