Answer
$$0.234{\text{ k}}{{\text{m}}^2}$$
Work Step by Step
$$\eqalign{
& a = 0.{\text{913 km}},b = 0.{\text{816 km}},c = 0.{\text{582 km}} \cr
& {\text{First}},{\text{ find the semiperimeter }}s \cr
& s = \frac{1}{2}\left( {a + b + c} \right) \cr
& s = \frac{1}{2}\left( {0.913 + 0.816 + 0.582} \right) \cr
& s = 1.1555 \cr
& \cr
& {\text{Now use Heron's formula to find the area }}A \cr
& A = \sqrt {s\left( {s - a} \right)\left( {s - b} \right)\left( {s - c} \right)} \cr
& A = \sqrt {1.1555\left( {1.1555 - 0.913} \right)\left( {1.1555 - 0.816} \right)\left( {1.1555 - 0.582} \right)} \cr
& {\text{Use a calculator}} \cr
& A \approx 0.234{\text{ k}}{{\text{m}}^2} \cr} $$
