Two neon signs are turned on at the same time. both signs blink as they are turned on. one sign blinks every 9 second's. the other every 15 seconds. in how many seconds will they blink together again

You coordinate volunteers for litter cleanup in local parks. your spreadsheet lists drivers and the number of seat belts in each driver’s car. the spreadsheet calculates the number of drivers (d) and the total number of seat belts (s). you want to know the maximum number of volunteers, besides drivers, that can be transported to the park in a single trip given that each person must have a seat belt of their own.