subtract:
7-z/z-5 - 4z-9/5-z
I am sure you meant:
(7-z)/(z-5) - (4z-9)/(5-z)
= (7-z)/(z-5) + (4z-9)/(z-5)
= (7-z + 4z-9)/(z-5)
= (3z-2)/(z-5)
7-z/z-5 - 4z-9/5-z
(7-z)/(z-5) - (4z-9)/(5-z)
= (7-z)/(z-5) + (4z-9)/(z-5)
= (7-z + 4z-9)/(z-5)
= (3z-2)/(z-5)