A person planning a weekend picnic trip should not spend more than 8 hours…

A person planning a weekend picnic trip should not spend more than 8 hours driving in total for the round trip (going and returning on the same day). The average speed of the forward journey is 40 km/hr. Due to traffic on the return (a Sunday), the average speed of the return journey is 30 km/hr. How far can he select a picnic spot?