There are 5 shapes on a 4x4 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, 3)
Distance from target shape to cyan right_triangle at (0, 3): 3
Distance from target shape to blue trapezoid at (0, 0): 6
Distance from target shape to yellow rectangle at (3, 1): 2
Distance from target shape to brown right_triangle at (0, 2): 4
Closest shape is the yellow rectangle at (3, 1) with distance 2</think>

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