Answer:
C
Step-by-step explanation:
The area of the triangle can be calculated using formula
[tex]A=\sqrt{p(p-a)(p-b)(p-c)},[/tex]
where p is half of the perimeter.
1. If a=19, b=20 and c=21, then
[tex]p=\dfrac{a+b+c}{2}=\dfrac{19+20+21}{2}=30\ m.[/tex]
2. The area is
[tex]A=\sqrt{30\cdot (30-19)(30-20)(30-21)}=\sqrt{30\cdot 11\cdot 10\cdot 9}=30\sqrt{33}\approx 172\ m^2.[/tex]
