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 (6, 7)
Distance from target shape to yellow rectangle at (5, 5): 3
Distance from target shape to red trapezoid at (5, 2): 6
Distance from target shape to green square at (1, 3): 9
Distance from target shape to purple rectangle at (6, 4): 3
Closest shape is the yellow rectangle at (5, 5) with distance 3</think>

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