Question

What should be added to (6x + 7y) to get (9x-5y)?​

Answer 1

$6x + 7y+ a = 9x - 5y \\ = >a = 9x - 5y - 6x - 7y \\ => a = 3x - 12y$

Hence,

(3x-12y) should be added to (6x + 7y) to get (9x-5y).