Can you pls answer the question below

Can someone explain the elimination method to me for this problem?

Write an expression that has three terms and simplifies to 4x - 7. identify the coefficient(s) and constant(s) in your expression

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