The demand for a commodity generally decreases as the price is raised. Suppose that the demand for oil (per capita per year) is $D(p)=800/p$ barrels, where $p$ is the price per barrel in dollars. Find the demand when $p=45$. Estimate the decrease in demand if $p$ rises to $46$ and the increase in demand if $p$ is decreased to $44$.

The demand $D(45)$ = .

The decrease in demand = barrels.

The increase in demand = barrels.