A rectangular prism with a volume of 6 cubic units is filled with cubes with side lengths 1/2 unit. How many 1/2 unit cubes does it take to fill the prism

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