Which is a unit rate?
A.47c for 2 pens
B. 20 gallons for 2 hours
C.15 hours for 3 months
D.18 miles driven in a week

D. 18 miles driven in a week.

Step-by-step 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.