Table:
Number of roofs	Number of sparrows

1	10

2	20

3	30

4	40

5	50

6	?

Provide the content of the cell located in row 4 and column 2 of this table. Output the target cell content as JSON in the format {"row_id":"m", "column_id":"n", "cell_value":"<Corresponding Cell Value>"}.

The target cell value in row 4 and column 2 is {"row_id":"4", "column_id":"2", "cell_value":"30"}.