Two friends take a drive around the city. when they get home, they look at the odometer and their watches, and determine they traveled 54 miles in 72 minutes. what was their average speed in miles per hour?

X miles per hour means that  x miles / 60 minutes 
If they traveled 54 miles / 72 minutes, so:
72 minutes - 60 minutes = 12 minutes 

60 minutes = 1 
12 minutes = 0,2  
1 + 0,2 = 1,2 hour
V = s/t 
v - velocity or speed
s - linear distance traveled 
t - time, so...
 we must divide 54 miles by 1,2 hour = 
Now, as we all know...
Their average speed was 45 miles per hour.

Hello!
your answer should be c