This math topic focuses on calculating elapsed time, including scenarios with negative time changes. The main skill practiced is determining the new time after subtracting half-hour increments from a given starting time, enhancing the understanding of time measurement and calculations. Each question presents a problem involving a clock and asks for the resulting time after a specific decrement, with multiple-choice answers provided for each scenario. This allows learners to develop proficiency in working with time and understanding its practical applications in everyday situations.