A ChE student spends part of his day walking between classes, during which time he expends energy at an average rate of 584 W. The remainder of the day he is sitting in class, studying in library, or resting during break; during these activities, he expends energy at an average rate of I88 W. If he expends a total of 4 4x10^7 J energy in a 24-hour day, how much of the day did he spend walking?