A vehicle starting with a full tank uses two-thirds of the gasoline in its tank when it stops at a gas station and adds half a tank of gasoline and continues its journey.
When the vehicle has traveled 900 km from the beginning, its gasoline runs out.
Given that the vehicle's gasoline consumption is constant throughout the journey, how many km is the distance the vehicle traveled between the starting point and the gas station?
A) 300
B) 360
C) 400
D) 450
E) 480