I am looking for a train. The train should arrive by 21:00 and should leave on sunday
okay, where are you departing from?
I am departing from Cambridge.
Where are you heading to from Cambridge?
I'm trying to get to Broxbourne.
Train TR8736 leaves at 5:01 and arrives at 6:01.
Perfect. please book it for 3 people. 
I have it booked the reference number is IYHXK218 and the price is 42.96 GBP.
Great, thanks for your help.
Absolutely, have a great day!