Recall that
P = F v
where
P = power produced by the engine
F = magnitude of the component force supplied by the engine in the direction of the car's motion
v = speed of the car
Draw a free-body diagram for the car, and decompose all the forces acting on it into components that act parallel and perpendicular to the slope. The car moves parallel to the slope, so we only care about 2 forces: the parallel component of the car's weight, and the force provided by the engine.
By Newton's second law, since the car is moving at a constant speed,
∑ F = F - m g sin(12°) = 0
where m = 950 kg and g = 9.80 m/s². Solve for F :
F = m g sin(12°) ≈ 1935.658 N
The engine provides P = 6.5 × 10⁴ W, so the car's speed v is
v = P / F = (6.5 × 10⁴ W) / (1935.658 N) ≈ 33.6 m/s
which makes C : 34 ms⁻¹ the closest answer.