I think you mean  ( f / g) x  =
  
 f (x)  / g(x)  =
  
 [ 4x^2 + 19x  - 5 ]  /  [ 4x^2 - x ]     factor numerator / denominator
  
 Note..it you're having trouble factoring....try factoring the "easier" thing, first....this is the denominator
  
 [ 4x^2 + 19x - 5 ]  /  [  x (4x - 1 ) ]      guess that the numerator includes 4x - 1 as a factor
  
 [ ( 4x - 1) ( x + 5 ) ] [ x (4x - 1 ) ]
  
 Note that the numerator factors perfectly..."cancel" the  4x - 1  on top/bottom
  
 (x + 5 )  / x          x not equal to  0, 1/4
  
  
  
  
 