A boy and a girl are playing in a park. The only daughter of the maternal grandfather of the girl, is the sister of the boy's father. How is the boy related to the girl?
The weights of 4 boxes are 20, 40, 60 and 90 kilograms. Which of the following cannot be the total weight, in kilograms, of any combination of these boxes and in a combination a box can be used only once?