There are 3 shapes on a 6x6 grid. Which shape is closest to the red right_triangle 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 right_triangle at (3, 1)
Distance from target shape to green rectangle at (5, 2): 3
Distance from target shape to brown right_triangle at (1, 5): 6
Closest shape is the green rectangle at (5, 2) with distance 3</think>

<answer>(5, 2)</answer>