7. Ferries Two high-speed ferries leave at the same time from Ft. Myers, Florida, going to Key West, Florida. The first ferry, the BigCat, travels at 34 miles per hour. The second ferry, the Atlantic Cat, travels at 28 miles per hour. In how many hours will the two ferries be 6 miles apart?

13. Walkie-Talkies Willie and Shanna have walkie-talkies that have a range of 16.8 miles. Willie and Shanna start at the same point and walk in opposite directions. If Willie walks 3 miles per hour and Shanna walks 4 miles per hour, how long will it take before they are out of range?

35. Simple Interest Aleksandra invested $6000, part at 6% simple interest and part at 4% simple interest for a period of 1 year. How much did she invest at each rate if each account earned the same interest?