help

(4/(3x-6)) feet / (8/(9x-18)) seconds =  (4* (9x-18) / (8 (3x-6)) =   (36x -72)/(24x-48) = (3x-6)/(2x-4)  f/s    = 3/2 f/s

  **edited....misread Q ****

Speed= distance/time.

We plug in the given expressions for distance and time.

Speed=

 $\frac{\frac{4}{3x-6}}{\frac{8}{9x-18}}\\ =\frac{4}{3x-6}\cdot\frac{9x-18}{8}\\ =\frac{1\cdot3}{1\cdot2}\\ =\frac{3}{2}$

This is 3/2 feet per second.