Answer:
9N down
Step-by-step explanation:
The net force on the ball dropped has a magnitude of 9N and it is directed downward. 
Given; 
 Gravitational force = 10N down
 Air resistance = 1N up
Air resistance is an opposite force that acts against a body passing through air. It is a negative force. 
Gravitational force is a force acting on a body due to gravitational attraction of the earth.
 Net force = Gravitational force down - Air resistance up
 = 10N - 1 N
 = 9N down
The net force is 9N downward.