Step-by-step explanation:
the correct formula for this is the heron's formula
which states that s=√s(s-a)(s-b)(s-c). Where s is a+b+c all divided by 2
s=√(13.5-12)(13.5-9)(13.5-6)
s=√(1.5)(4.5)(7.5)
s=√50.625
s= 7.11 or 7 to the nearest square unit
