Why do this problem?
is one which could be done as an introduction when extending or revising work on time and clocks. It will encourage the use of digital times.
At what time is the first right angle after $12$ o'clock?
Why is it not just $15$ minutes later?
Can you write down these times using digital notation?
Why is the number of times not divisible by $4$?
Learners could find out the times for $24$ hours and record using $24$ hour digital notation.
Suggest counting round a clock, or using the interactive clock in the question.