To find the acceleration, we use the formula for power:

\(P = Fv\)

where \(P\) is the power, \(F\) is the force, and \(v\) is the velocity.

Rearranging for force, we have:

\(F = \frac{P}{v} = \frac{420}{5} = 84 \text{ N}\)

(i) For the horizontal road:

Using Newton's second law, \(F = ma\), we have:

\(84 = 75a\)

\(a = \frac{84}{75} = 1.12 \text{ m/s}^2\)

(ii) For the inclined road:

The component of gravitational force along the slope is \(75g \sin(1.5^{\circ})\).

Using Newton's second law, \(F - 75g \sin(1.5^{\circ}) = 75a\), we have:

\(84 - 75 \times 9.8 \times \sin(1.5^{\circ}) = 75a\)

\(a = \frac{84 - 75 \times 9.8 \times \sin(1.5^{\circ})}{75}\)

\(a \approx 0.858 \text{ m/s}^2\)