The pattern of 9 shaded squares below faces a mirror along the dashed line MN on its right side.

Explanation

1. 01

   A mirror standing along MN, to the right of the grid, swaps left and right but not top and bottom: a square in column c moves to column $6 - c$ and stays in its row.

2. 02

   So the shaded squares (1, 4), (1, 5), (2, 3), (2, 4), (2, 5), (3, 3), (3, 4), (3, 5), (4, 3) (row, column) move to (1, 1), (1, 2), (2, 1), (2, 2), (2, 3), (3, 1), (3, 2), (3, 3), (4, 3).

3. 03

   Figure 4 shows exactly these squares.