I have to simplify but I’m doing something wrong and when I looked it up it said used AC method which is a term I never heard in my class. Please help

Type the correct answer in the box. consider the system of linear equations below. rewrite one of the two equations above in the form ax + by = c, where a, b, and c are constants, so that the sum of the new equation and the unchanged equation from the original system results in an equation in one variable.