A cyclist is riding from the city to the country. She rides 20 miles each hour. At the beginning of the 1st hour, she is 10 miles away from the city center. At the beginning of the 2nd hour, she is 30 miles away from the city center. Write an explicit formula to show her distance from the city at any given hour. Then use the formula to find her distance at the beginning of the 5th hour.​