There are 5 shapes on a 8x8 grid. Which shape is closest to the gray 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: gray right_triangle at (3, 6)
Distance from target shape to red square at (1, 6): 2
Distance from target shape to purple square at (5, 0): 8
Distance from target shape to blue right_triangle at (6, 7): 4
Distance from target shape to yellow rectangle at (7, 4): 6
Closest shape is the red square at (1, 6) with distance 2</think>

<answer>(1, 6)</answer>