You can put this solution on YOUR website!
Note in this question that there are two things to convert: kilometers into miles, and seconds into hours. Let's deal with kilometers into miles first. We need to know how many miles are in a kilometer. This can be done with a simple web search: 0.621 miles is 1 kilometer. So
250 km/sec * 0.621 miles/km = 155.25 miles/sec (the km cancel out)
Next, we need to convert from seconds into hours. Well, there are 60 sec in a minute and 60 minutes in an hour, so there are 60*60=360 sec/hr. Thus,
155.25 miles/sec * 360 sec/hr = 55890 miles/hr.