First, convert 625 revolutions per minute to revolutions per hour: 625*60=37500 revolutions per hour
Next you can simplify 88 feet for 11 revolutions to 8 feet per revolution.
To find how many feet per hour you are travelling, multiply 37500 by 8 ft., which results in 300000 feet per hour.
Then you have to convert 300000 ft. per hour to mph. There are 5280 feet in a mile, so divide 300000 by 5280 to get approx. 57 mph.