What is the least common multiple for the numbers 4 and 5

If m 17 27 90 63 ** picture is attached

Jack has a piece of red ribbon that is two times as long as his piece of blue ribbon. he says that he can use two different equation to find out how long his piece of red ribbon is compared to his piece of blue ribbon is. is he correct? explain his reasoning

You paid 28.00 for 8 gallons of gasoline. how much would you pay for 15 gallons of gasoline?