(a) Using Newton's second law, the net force is given by:

\(F - 900 = 4000 imes 0.5\)

Solving for the driving force, F:

\(F = 900 + 4000 imes 0.5 = 2900 ext{ N}\)

(b) The power required to maintain a constant speed is given by:

\(P = F imes v\)

Here, the force F is the resistance, 900 N, and the speed v is 25 m/s:

\(P = 900 imes 25 = 22500 ext{ W} ext{ or } 22.5 ext{ kW}\)