(a) To find the tension \(T\) in the tow-bar, consider the forces acting on the trailer. The trailer has a mass of 400 kg and is accelerating at 1.5 \(\text{ms}^{-2}\). The net force on the trailer is given by Newton's second law:

\(T - 100 = 400 \times 1.5\)

Solving for \(T\):

\(T = 400 \times 1.5 + 100 = 700 \text{ N}\)

(b) To find the power of the engine, first calculate the total force \(F\) exerted by the engine. The car and trailer together have a total mass of 2200 kg. Using Newton's second law for the entire system:

\(F - 250 - 100 = 2200 \times 1.5\)

\(F = 2200 \times 1.5 + 250 + 100 = 3650 \text{ N}\)

The power \(P\) is given by the product of the force and the velocity:

\(P = Fv = 3650 \times 20 = 73,000 \text{ W}\)

Therefore, the power of the engine is 73,000 W or 73 kW.