Use Heron's formula to find the area of the triangle since you're given all the side lengths.
Heron's formula: [tex] \sqrt{s(s-a)(s-b)(s-c)} [/tex], where s = [tex] \frac{a + b + c}{2} [/tex].
Find s.
[tex] \frac{19 + 21 + 15}{2} [/tex] = 27.5
Now plug in s and a, b, and c into the formula.
[tex] \sqrt{27.5(27.5-19)(27.5 - 21)(27.5 - 15)} [/tex] = 137.8
The area of the triangle is 138 square meters.