How to design a sample in Symphony2?

Question

symfony

There are two entities in the
Trip database - travel options from different places
Car - car class (restriction on the number of passengers)

Now the booking process
A person indicates where and where he is going and how many passengers
the result of the work should look like a list of prices
for example: from an address to a railway station 1 person

I can get a list of trips (Trip)
then a list of cars (Car)
and now how do I need to take a car and get the corresponding price
how can I do this?