Final answer:
The question, though incomplete, relates to a mathematical problem where coffee has been spilled on a m×n rectangular grid, likely requiring the use of combinatorics or geometry to solve.
Step-by-step explanation:
It appears part of the original question is missing, but based on the context given, the subject involves solving a problem where coffee has been spilled on a m×n rectangular grid of squares, and the objective may be to find a way to salvage or reconstruct a portion of the grid that is unstained for use. This type of problem typically involves combinatorics or geometry, which are branches of mathematics concerned with counting, arrangement, and spatial structures, respectively.
To solve such a problem, one would normally determine the arrangement and number of stained squares and then look to find a suitable subgrid (a smaller rectangle within the larger grid) that is free of stains. This might involve various mathematical strategies, including calculations to maximize the size of the stain-free subgrid or to minimize the area lost due to stained squares.