There are 5 shapes on a 4x4 grid. Which shape is closest to the blue 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: blue rectangle at (3, 0)
Distance from target shape to gray trapezoid at (2, 1): 2
Distance from target shape to green right_triangle at (2, 3): 4
Distance from target shape to red rectangle at (3, 2): 2
Distance from target shape to purple rectangle at (3, 1): 1
Closest shape is the purple rectangle at (3, 1) with distance 1</think>

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