Answer:
When we know all 3 sides, we use Heron's Formula
area = sqrt [s *(s-a) * (s-b) * (s-c)]
where "s" is the semi-perimeter which in this case equals
s = (6 + 8 + 12) / 2 = 13
area = sqrt [13 * 5 * 7 * 1]
area = sqrt 455
area = 21.3307290077
area = 21.33 square feet (rounded)
Step-by-step explanation:
