Help me please with this

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

3x = 729 solve for x plz . it's urgent. will mark

Arectangle has a length of 6cm by 8cm what is the length of a diagonal of the rectangle