Heron's formula:
Triangle Area =√[s(s-a)(s-b)(s-c)]
Where s = half of the perimeter of the triangle (in our case =36/2=18)
a, b, & c the length of each side (in our case all sides are equal since it's an equilateral triangle with a perimeter = 36 or each side =36/3 =12)
Now we can apply Heron's formula:
Area =√[18(18-12)(18-12)(18-12] =√[18x6x6x6] =√(3888) = 62.354 cm²
or rounded =62 cm²