Trigonometry questions?

A signal buoy in this Chesapeake Bay bobs up and down with the height h of its transmitter (in feet) above sea level modeled by h = a sin bt + 5. During a small squall its height varies from 1 feet to 9 feet and there are 3.5 seconds from one 9-feet height to the next. what are the values of the constants a and b?