A 100-kg student eats a 200-calorie doughnut. To 'burn off the sugar high', he decides to climb the steps of a tall building. How high would he have to climb to expend an equivalent amount of work? (1 food calorie = 10³ calories 4200 J).
a) 273 m; b) 428 m; c) 857 m; d) 8400 m.