I don't understand how to do the question.

I believe, the best answer will be: given equation does not have any solutions, because for any value of x we will get 109 = 89 , which is false statement.

x + 109 = x + 89

- x - x

109 = 89 , but 109 ≠ 89

x + 109 = x + 89

- x - x

109 = 89 , but 109 ≠ 89