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

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