This problem could be used as an extension task once students have learnt to draw reflections accurately. It can provide a valuable mathematical challenge for students who are ready to move on while others in the class need more practice with their basic drawing skills.
Alternatively, this problem and the two related problems ...on the Wall , and Who Is the Fairest of Them All? could form a unit of work on combined transformations. All three problems ask students to consider the effect of combining two transformations, and then challenge them to describe the single transformations that produce the same results.
This printable resource may be useful: Mirror, Mirror...,
As an extension task, all that is needed is to provide the problem as a worksheet to a pair of students who make sense of it together. When they have established the combined transformation for one specific example, a teacher intervention may be appropriate, to move the focus to the general case - asking the key questions below.
With a full class, encourage different students to start with slightly different spacings of parallel lines and flag positions. The teacher intervention above could become a full class discussion. Students could regroup according to similarities/differences in the final combined transformations in order to acquire more information without needing to do a lot more drawing.
Ensure students use squared paper and encourage them to draw their reflections accurately.