Answer:
3/5 of the journey is (90 km/h)(5 h) = 450 km, so 1/5 of the journey is 150 km. It follows that the journey is 750 km, meaning Elliot has 300 km left to drive. At that point, he reduces his speed to
75 km/h.
300 km/(75 km/h) = 4 hours.
So Elliot took 9 hours to complete his journey.