Car and truck velocity question

[vicsic]

Question:
A car is initially 4.0km/h south of a gas station and is moving at a constant speed of 55km/h due north. A truck is initially 6.0km north of the gas station and is moving at a constant speed of 45km/h due south. How far are the vehicles from the gas station when they pass each other?

Formulas:
V=d/t

Attempt at solution:
So I said:

Car
D=4.0km south
V=55km/h north

Truck
D=6.0km north
V= 45km/h south

Now I had the idea of making the times equal,

So I calculated the time for the car:
Tcar= d/v = 4.0/55= 0.073h
Ttruck = d/v = 6.0/45=0.13h

From here I am stuck I tryed subtracting the times, but could get any further. Help from this point would be awesome.

I have done a little diagram attached

 

[mfb]

You calculated the time difference as seen at the gas station. This is not relevant for the task here.
Can you express their position as function of time?

 

[vicsic]

Would that be t=d/v=d/v??

 

[mfb]

That would be the time to travel some specific distance.
No, what I mean is an equation of the type x(t)=...
You plug in the time t, and get the position x (relative to the gas station) at that time t.

 

[vicsic]

like x(t)=changeinD/change in v

 

[mfb]

There is no change in v.

A simple example: Imagine I start 10km in front of from the gas station (seen by an arbitrary direction) and move with 20km/h. In that case, my position is given by x(t)=-10km + 20km/h*t
For t=0, this givex x(0)=-10km, as expected.
1/2 hour later, I am at x(1/2 h)=-10km + 20km/h * 1/2 h = -10km + 10km = 0 - in other words, directly at the gas station.

Can you find similar equations for your vehicles?
Afterwards: What means "passing" for their positions?