Answer
1 cougar per 150 $mi^2$
Work Step by Step
First find the actual amount of land by subtracting out the area covered in water.
living area = $45000\ mi^2-3000\ mi^2=42000\ mi^2$
Next find the ratio and reduce to lowest terms.
$\frac{280\ cougars}{42000\ mi^2}=\frac{280\div280\ cougars}{42000\div280\ mi^2}=\frac{1\ cougar}{150\ mi^2}$
