Question

(11x + 9) − (?) = 6x + 8. Which expression is missing?

Answer 1

The missing expression is 5x + 1 because 11x is 5x more than 6x and 8 is 1 more than 9,and the missing expression is being subtracted from 11x + 9. 
Hope this helps!

Answer 2

Subtract the terms on the right from the terms on the left to determine missing expression

11x - 6x= 5x
9-8= 1

Missing expression= 5x + 1

(11x + 9) − (5x + 1) = 6x + 8
(11x - 5x) + (9 - 1)= 6x + 8
6x + 8= 6x + 8

ANSWER: 5x + 1

Hope this helps! :)