A man with a mass of 60 kg steps into powdery snow and sinks to his waist. The area of each man's feet is 250 centimeters squared. He put on skis, each of which has an area of 1800 centimeters squared. What pressure does each of his feet exert on the snow? What pressure does each of his skis exert on the snow? Explain why he can ski on snow and not walk on it.