The figure is made up of 16 identical squares. There are 5 shaded squares in the figure. Shade 3 more squares to form a symmetric figure with AB as the line of symmetry.

1. Identify the line of symmetry and the positions of the currently shaded squares.

The line of symmetry $AB$ is the main diagonal from top-left (Row 1, Col 1) to bottom-right (Row 4, Col 4).
The currently shaded squares are:

• $(1, 1)$ (on the line of symmetry)
• $(1, 4)$
• $(2, 4)$
• $(3, 2)$
• $(4, 4)$ (on the line of symmetry)

2. Find the reflection of each shaded square across the diagonal $AB$.

For a diagonal line of symmetry from top-left to bottom-right, the reflection of a square at Row $r$, Column $c$ is at Row $c$, Column $r$.

• $(1, 1)$ reflects to $(1, 1)$ (already shaded)
• $(1, 4)$ reflects to $(4, 1)$
• $(2, 4)$ reflects to $(4, 2)$
• $(3, 2)$ reflects to $(2, 3)$
• $(4, 4)$ reflects to $(4, 4)$ (already shaded)

3. Identify the 3 squares to be shaded.

The 3 new squares to shade are $(4, 1)$, $(4, 2)$, and $(2, 3)$.