Equivalent land area of 600 mm^2 map-area with given map-scale

$A_\text{map} = 600 \text{ mm}^2 \left( \dfrac{1 \text{ m}}{1000 \text{ mm}} \right)^2$

$A_\text{map} = 0.0006 ~ \text{m}^2$
 

By similar figures
$\dfrac{A_\text{park}}{A_\text{map}} = \left( \dfrac{40,000}{1} \right)^2$

$\dfrac{A_\text{park}}{0.0006} = \left( \dfrac{40,000}{1} \right)^2$

$A_\text{park} = 960,000 ~ \text{m}^2$

$A_\text{park} = 96 ~ \text{ha}$   ←   answer