There are 5 shapes on a 6x6 grid. Which shape is closest to the green 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: green right_triangle at (4, 0)
Distance from target shape to yellow right_triangle at (3, 2): 3
Distance from target shape to purple right_triangle at (4, 4): 4
Distance from target shape to gray rectangle at (3, 1): 2
Distance from target shape to brown trapezoid at (4, 2): 2
Closest shape is the gray rectangle at (3, 1) with distance 2</think>

<answer>(3, 1)</answer>