Answer:
V = 66 mph
Step-by-step explanation:
To calculate the speed, we need to use the following expression:
V = d/t
d: distance
t: time
Distance is in miles, while time is in seconds, however, we will convert this to hour for a better understanding.
30 minutes is half an hour or 0.5 h. This can be calculated also like this:
t = 30 min / 60 min/h = 0.5 h
Now, to get the distance travelled by Sara's mom, we just need to substract the marker 88 with the exit mile which is 121 so:
d = 121 - 88 = 33 mi
Finally, let's just replace distance and time in the first expression above:
V = 33/0.5
V = 66 mi/h
This is the average speed