There are 5 shapes on a 9x9 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 (3, 8)
Distance from target shape to gray rectangle at (7, 0): 12
Distance from target shape to brown rectangle at (5, 1): 9
Distance from target shape to red right_triangle at (7, 2): 10
Distance from target shape to yellow trapezoid at (1, 3): 7
Closest shape is the yellow trapezoid at (1, 3) with distance 7</think>

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