Solve the problem.
Before exercising, an athlete measures her air flow and obtains a = 0.65 sin

where a is measured in liters per second and t is the time in seconds. If

the athlete is inhaling; if

the athlete is exhaling. The time to complete one complete inhalation/exhalation sequence is a respiratory cycle. Find the values of t for which the athlete's air flow is zero. Find all values of t for

seconds.