There are 5 shapes on a 6x6 grid. Which shape is closest to the gray 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: gray rectangle at (5, 1)
Distance from target shape to brown rectangle at (3, 3): 4
Distance from target shape to green rectangle at (1, 3): 6
Distance from target shape to pink right_triangle at (1, 5): 8
Distance from target shape to purple trapezoid at (0, 1): 5
Closest shape is the brown rectangle at (3, 3) with distance 4</think>

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