There are 4 shapes on a 7x7 grid. Which shape is closest to the red 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: red rectangle at (1, 5)
Distance from target shape to blue trapezoid at (6, 1): 9
Distance from target shape to purple rectangle at (3, 1): 6
Distance from target shape to yellow right_triangle at (5, 1): 8
Closest shape is the purple rectangle at (3, 1) with distance 6</think>

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