Firstly, find amount km which Aaron realises that he forgot textbook: 5/6*6/10=1/2 km. He must walk the same distance to return to the home: additional 1/2km. And the last part is length of the way to school: 6/10 km. Therefore the total distance which Aaron walked is: 1/2+1/2+6/10=16/10=1.6 km.