Factor completely 9ab + 12ax − 6b − 8x.

prime

(3b − 4x)(3a − 2)

(3b + 4x)(3a − 2)

(3b + 4x)(3a + 2)

Okay so you split 9ab + 12ax - 6b - 8x 
             into two 2-term polynomials 
              + 12ax + 9ab   and     - 6b - 8x
             doesn't look that good to me so lest try other one : 
             9ab + 12ax   and     - 6b - 8x
              looks good for now 

            Pull out from each binomial separately
             9ab + 12ax   =   3a • (3b + 4x)
              - 6b - 8x   =    - 2 • (3b + 4x)

           Add up to arrive at the desired factorization so now you have
             (3a - 2) • (3b + 4x)

Hope that Helped!