Net horizontal force is zero at constant velocity, but driving force calculation doesn't match options

Steps:

• The car moves at constant velocity, so by Newton's first law, net (total) horizontal force = 0 N.
• Engine efficiency η = 0.6; input power P_in = 900 W, so mechanical output power P_out = η × P_in = 540 W.
• If "total horizontal force" means magnitude of driving (or resistive) force, then P_out = F × v, so F = P_out / v = 540 / 12 = 45 N.
• Since 45 N and 0 N are not options, the question is ambiguous.

Why B is correct:

• Not applicable; calculation yields 45 N for driving force.

Why the others are wrong:

• A: Might result from wasted power (0.4 × 900 / 12 ≈ 30 N, close but incorrect).
• C: From input power without efficiency (900 / 12 = 75 N, approximate).
• D: Exceeds possible output (would require >100% efficiency).

Not enough information. Final answer: Not enough information.