help me this plss.

1. Alvin can do a given job in 4 hours. Armando can do the same job in 9 hours. Armando begins working and after 1 hour is joined by Alvin. In how many hours will they complete the job? 2. Von can do a piece of work in 60 days, which Johnmar can do in 40 days. Both started the work but Von left 10 days before the completion of the work. How many days does the work was finished? 3. Jeffrey and Daniel compete for a stretched of 20 km long. It took 40 seconds for Jeffrey to reach the finish line and Daniel 50 seconds to reach the finish line. How far was Daniel behind when Jeffrey reaches the finish line? 4. A speedboat can make a trip of 100 miles in one hour and 30 minutes if it travels upstream. If it travels downstream, it will take one hour and 15 minutes to travel the same distance. What is the speed of the boat in calm water? 5. Donn can paint a fence 50% faster than Peter and 20% faster than Jan David. Together they can paint a given fence in four hours. How long will it take Donn to paint the same fence if he had to work alone? 6. The time required for two examinees to solve the same problem differ by two minutes. Together they can solve 32 problems in one hour. How long will it take for the slower problem solver to solve the same