In summary: Going up, the engine produces 44 hp more power to sustain the constant velocity than it does going down the same hill. At what angle is the hill inclined above the horizontal? Going up a hill, the car's engine produces 44 hp more power to sustain the constant velocity than it does going down the same hill. The angle at which the hill is inclined above the horizontal is 45 degrees.
Right. (1 hp = 746 W the last I checked, but who's counting?) [OK, just checked, it's 745.699872 W for 1 "mechanical hp" and exactly 746 W for "electrical hp". Trivia for the day.]