To reflect the figure, we need to reflect its vertices to the opposite side of line ℓ in a way such that the distance from the vertices to line ℓ remains the same. Let's in the diagram draw lines that are perpendicular to the line ℓ and that go through the vertices of the figure.
Now, we will locate each reflected point the same distance from line ℓ on the opposite side.
To complete the reflection, we will finally connect the reflected points and shade the lower part of it to have its image.