There are 3 shapes on a 6x6 grid. Which shape is closest to the green rectangle in terms of Manhattan distance? The final answer is the grid position of the closest shape like (row_index, column_index).
<think>Target shape: green rectangle at (0, 0)
Distance from target shape to blue rectangle at (5, 3): 8
Distance from target shape to red square at (3, 1): 4
Closest shape is the red square at (3, 1) with distance 4</think>

<answer>(3, 1)</answer>