There are 3 shapes on a 4x4 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, 3)
Distance from target shape to brown right_triangle at (0, 1): 3
Distance from target shape to pink right_triangle at (3, 3): 2
Closest shape is the pink right_triangle at (3, 3) with distance 2</think>

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