Question 253271
Well to go from miles per hour to feet per second we need to know how many feet there are in a mile and how many seconds there are in an hour. There are 5280 feet in 1 mile and 3600 seconds (1hour times 60 minutes times 60 seconds) in 1 hour.

70 miles per hour mean that the Car A is travelling 70*5280 feet per hour. which is 369600 feet per hour. We want to know the how many feet the Car A travels per second. So we divide 369600 by 3600 to give 102 and 2/3 feet per seond.

We do the same for Car B. 55*5280/3600=80 and 2/3 feet per second. 

So the difference between the two cars is 102 and 2/3 feet per second minus 80 2/3 feet per second which is 22 feet per second.