A couple of pre cal questions need help with

1. A buoy bobs up an down with the height H of its transmitter in feet above sea level modeled by h=a sin b t +5. The height varies from 1 ft to 9 ft and it takes 3.5 sec from 9 ft to the next peak. What are the constants a and b?

So far I got to -5=9*sin(b*3.5)

2. A ferris wheel 50 ft in diameter makes one revolution every 40 sec. IF the center is 30 ft above the ground how long after reaching the low point (5 ft above ground) does it take to reach 50 ft above the ground.

I really don't know what to do on this one. I know the circumference and ft a second. But I can't translate that to 50 ft above the ground.

3. A tsunami hit and caused waves that travel at 540 ft sec and reach a height of 60 ft. IF the period is 30 minutes estimate the length between the crests.

In completely lost on this one..