The weights of 4 boxes are 20, 40, 50 and 30 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?
In a certain code, 327 means 'don't cut tree', 635 means 'plant one tree', 138 means 'tree gives shade' and 4953 means 'we must plant tree'. Which digit represents 'shade'?