Remark
You can use a method called unit analysis to solve this problem. You will use it many times in your education later on.
Solve
[tex]\dfrac{28 mile}{hour} *\dfrac{5280 feet}{mile}*\dfrac{1 hour}{60 min}*\dfrac{1 min}{60 sec}[/tex]
Now sort out the numbers in the numerator and those in the denominator and multiply them together.
Numerator 28 * 5280 * 1 * 1 = 147840
Denominator: 60 * 60 = 3600
Now divide the numerator by denominator
Answer = 147840 / 3600 = 41.1 Feet / second
28 miles per hour = 41.1 feet / second