Explanation:
140 * 5280 = ???
(Miles) * (Feet)
??? * 3600 = ???
(answer from before) * (seconds in a hour)
You need to convert it. When converting to a smaller unit multiply. Since there are 3,600 seconds in an hour, multiply you answer to that.
Hope this helps! I cannot give you that answer, but here's a explanation on how to solve it. :)