The rocket that carried the Curiosity Rover to Mars traveled at a speed of 21,000 miles per hour. What is this speed to the nearest mile per second?

Well, think of it this way ... The rocket is traveling 21,000 miles for every 60 min.

So, divide 21,000 by 60 and you get 350. So, it travels 350 miles per minute, or every 60 seconds. 350 divided by 60 seconds is 5.833333333. So, your answer would be 5.8