A signal buoy in the chesapeake bay

A signal buoy in the 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 ft to 9 ft and there are 3.5 sec from one 9-ft height to the next.
What are the values of the constants a and b?