Answer:
a) the number of miles in 1 kilometer
Step-by-step explanation:
The car converts from miles/hour to kilometers/hour, if we see the time measurement (hours) it stays the same in both units.
So to make the conversion<u> it is enough to know how many miles are in one kilometer.</u>
For example, lets convert 10miles/hour to kilometers/hour.
there are 0.621371 miles in 1 kilometer, so if we divide 10miles/hour by 0.621371 we get kilometers/hour units:

Thus to make the conversion between the two units is needed the number of miles in 1 kilometer.