#### Answer

The population density in 1980 was $25.0~people/km^2$

#### Work Step by Step

We know that $1~mi = 1.6~km$
Then: $1~mi^2 = 1.6~km\times 1.6~km = 2.56~km^2$
In 1980, the land area was $3,539,289~mi^2$. We can convert this area to units of $km^2$.
$3,539,289~mi^2 = \frac{3,539,289~mi^2}{1}\times \frac{2.56~km^2}{1~mi^2} = 9,060,579.84~km^2$
We can find the population density in 1980.
$\frac{226,545,805~people}{9,060,579.84~km^2} = 25.0~people/km^2$
The population density in 1980 was $25.0~people/km^2$