Answer:
D. 18 miles driven in a week.
Explanation:
A unit rate describes how many units of the first type of quantity corresponds to one unit of the second type of quantity.
a. 47 c for 2 pens
thus the price is for 2 pens and not 1.
b. 20 gallons or 2 hours
Thus the amount of gasoline used is for 2 hours and not 1.
c. 15 hours for 3 months
Thus the time given is for 3 months.
d. 18 miles driven in a week
The distance given is for 1 week and thus is the unit rate.
Thus unit rate is 18 miles driven in a week.