Q: A Spaceship lands on a new planet. The crew decides to measure the speed of sound by blowing across one end of a tube. The tube is 50cm long, and the crew finds one resonant frequency at 1620Hz and the next resonant frequency at 1980Hz. What is the speed of sound? What is the number of each of the harmonics they found? What type of tube is the crew using- open/open, or open/closed?

I found the speed to be 360 m/s, but I have no idea how to find the harmonics! I don't know where to start! Help!