The blades of a helicopter exert an upward force of 25,000 Newtons. The mass of the helicopter is 2,000 kg. What is the acceleration of the helicopter?

Use newtons second law where a force downward is negative and upward is positive.
Newtons second law is:
F_(n e t)=sum_i F_i=m a
Which just says the sum of the net force is equal to the sum of the individual forces thats equal to the mass times the acceleration.
Now let F_h be the upward for due to the helicopter and F_g be due to gravity. Then we know:
F_(n e t) =F_h-F_g=F_h-mg=ma
Solve for a.
(F_h-mg)/m=a
Plug in the values and let the acceration for gravity g be 10 m/s/s.
(25,000 N-2,000 kg *10 m/s^2)/(2,000 kg)=a
(25,000 N-2,000 kg *10 m/s^2)/(2,000 kg)=a
(25,000 N-20,000 N)/(2000 kg)=a
(5,000 N)/(2,000 kg)=a
5/3 (m/s^2) =a
Therefore the acceleration of the helicopter is 5/3 meters per second per second upwards.
https://www.physicsclassroom.com/class/newtlaws/Lesson-2/Drawing-Free-Body-Diagrams