There are 5 shapes on a 7x7 grid. Which shape is closest to the red rectangle in terms of Manhattan distance? The final answer is the grid position of the closest shape like (row_index, column_index).
<think>Target shape: red rectangle at (4, 3)
Distance from target shape to purple rectangle at (1, 2): 4
Distance from target shape to blue square at (3, 0): 4
Distance from target shape to green right_triangle at (3, 1): 3
Distance from target shape to brown trapezoid at (0, 3): 4
Closest shape is the green right_triangle at (3, 1) with distance 3</think>

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