Answer
$$684.631{\text{ }}{{\text{m}}^2}$$
Work Step by Step
$$\eqalign{
& a = {\text{43 m}},b = {\text{32 m}},c = {\text{51 m}} \cr
& \cr
& {\text{First}},{\text{ find the semiperimeter }}s \cr
& s = \frac{1}{2}\left( {a + b + c} \right) \cr
& s = \frac{1}{2}\left( {43 + 32 + 51} \right) \cr
& s = 63 \cr
& \cr
& {\text{Now use Heron's formula to find the area }}A \cr
& A = \sqrt {s\left( {s - a} \right)\left( {s - b} \right)\left( {s - c} \right)} \cr
& A = \sqrt {63\left( {63 - 43} \right)\left( {63 - 32} \right)\left( {63 - 51} \right)} \cr
& {\text{Use a calculator}} \cr
& A \approx 684.631{\text{ }}{{\text{m}}^2} \cr} $$
