So to begin your problem, you know that your car already has an average which is 65km/45 mins. The problem wants you to change this to km/hr. This means that you need to convert minutes to hours. A simple way to do this is by using fractions.
Set your problem up with fractions similar to this:
65km/45 mins x 60 mins/1 hr.
the whole point is to cancel out your minutes, and leave the hours as your new unit for the denominator
65km/45 x 60/1 hr.
now you want to reduce (I divided the first fraction by 5)
13km/9 x 60/1 hr.
780km/9hrs.
That would be your answer. If someone can double check my math that would be fantastic.