There are 6 shapes on a 8x8 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 (6, 6)
Distance from target shape to cyan rectangle at (1, 6): 5
Distance from target shape to blue right_triangle at (1, 3): 8
Distance from target shape to purple rectangle at (7, 0): 7
Distance from target shape to green right_triangle at (5, 4): 3
Distance from target shape to yellow square at (7, 1): 6
Closest shape is the green right_triangle at (5, 4) with distance 3</think>

<answer>(5, 4)</answer>