I think you want to ask "How long does it take?" not "How fast does the ball travel?". You already know that the ball travels at 90 mi/hr.
In the two quantities you have the distance is stated in different units, one in feet and the other in miles. You need them in the same units. There are 5280 feet in a mile so
90 mi/hr is 5280 90 = 475200 feet/hr
Now the units tell you what to do. You have two quantities, one in distance units (feet) and the other is distance over time units ( feet/hr) and you want a time. Thus to get time you can do the following
feet hours/feet = hours
60.5 1/475200 = 0.00012732 hours.
This is a small time but it doesn't take long to go 60.5 feet at 90 mi/hr. There are 60 minutes in an hour so
0.00012732 hours = 60 0.00012732 = 0.0076389 minutes
This is still a small number so express it in seconds.
0.0076389 minutes = 60 0.0076389 = 0.458 seconds.