Use the lowest common denominator to subtract the following rational expressions

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

2x minus y equals 6, x plus y equals negative 3

Gabrielle's age is two times mikhail's age. the sum of their ages is 84. what is mikhail's age?