The answer is 7, It's a simple extension of the Magic Calculator trick.
Each card represents a bit, with the upper left index value being the value of that bit.
To perform it as a trick, you ask the volunteer to pick a number between 1 and 64, and hand you the cards on which their number appears. Add up the index values on the selected cards, and you have ...
I may need some clarification on counting but I think I've found a solution in which the landlord needs to repair 38 squares while filling just 3 other apartments with water.
Beginning of answer (?)
This time around, the pawns are the obstacle, as they can move forward to defend all while being promoted
What a cruel little sister though, she could have ended his misery with just one move starting with this board !